Abstract: Mechanical cotton topping required stable canopy height acquisition and selective terminal-bud removal under nonuniform field conditions. Rigid cutting devices often caused excessive stalk injury, whereas visible-light vision methods were easily affected by illumination variation, canopy gaps, and leaf occlusion. This study developed a rolling-grid cotton topping device driven by canopy point-cloud height fitting, and evaluated whether it could achieve real-time height profiling, flexible terminal-bud removal, and acceptable field performance for mechanized cotton production. A prototype was designed by integrating a high-clearance tracked chassis, an infrared binocular camera, a height-profiling mechanism, a rolling-grid topping mechanism, and a programmable logic controller control system. The camera acquired three-dimensional canopy point clouds by active infrared structured light. The point clouds were processed through spatial filtering, outlier removal, down-sampling, surface interpolation, median height extraction, and smoothing, and the fitted canopy height was then transmitted to the controller for real-time adjustment of the topping mechanism. During operation, the rolling grid screened large leaves outside the working area and guided terminal buds into the grid, where a nitrile rubber hob removed them through striking, bending, and pulling. Field tests were conducted in Changji, Xinjiang, using rubber thickness, compensation depth, cutter rotational speed, and vehicle speed as test factors. The height detection test showed that the fitted canopy height followed the fluctuation trend of manually measured plant height under field conditions. Compared with manual measurements, the mean absolute error was 33.03 millimetres and the root mean square error was 37.86 millimetres. The detected height was generally lower than the actual plant height because canopy gaps and surface fitting reduced the fitted profile. However, the detected value was close to the terminal-bud region and therefore suitable for height-profiling control. This result indicated that the point-cloud-based method provided a stable height input and reduced the dependence on visible-light image recognition. Field topping tests showed that the four operating factors significantly affected topping quality. Increasing rubber thickness enhanced terminal-bud removal because the hob became more rigid and transmitted greater impact force, but excessive rigidity also increased injury to tissues below the terminal bud. Increasing compensation depth allowed more terminal buds to enter the effective working area and improved the topping rate, but excessive downward compensation caused deeper stalk insertion and increased over-topping. Increasing cutter rotational speed strengthened the striking and breaking effect of the rubber hob, whereas too high a speed aggravated mechanical damage. Increasing vehicle speed reduced the topping rate because the profiling mechanism had less time to respond to plant-to-plant height differences. Response surface analysis showed that rubber thickness had the greatest influence on both topping rate and over-topping rate, followed by vehicle speed, cutter rotational speed, and compensation depth. The optimized parameter combination predicted by the model was close to a rubber thickness of 8 millimetres, compensation depth of 15 millimetres, cutter rotational speed of 700 revolutions per minute, and vehicle speed of 0.2 metres per second. After rounding the parameters for engineering implementation, verification tests produced an average topping rate of 83.66% and an average over-topping rate of 20.00%. The relative errors between measured and predicted values were 1.909% and 3.928%, respectively, confirming the reliability of the regression model and the feasibility of the optimized operating parameters. The results demonstrated that the rolling-grid structure effectively separated leaves from terminal buds, and that the rubber hob achieved flexible removal instead of rigid cutting. The developed rolling-grid cotton topping device realized coordinated canopy perception, profiling control, terminal-bud screening, and flexible removal. The study confirmed that canopy point-cloud height fitting could provide reliable height information for field profiling, and that the rolling-grid and rubber-hob mechanism was feasible for mechanized cotton topping. However, the over-topping rate remained relatively high because of fixed compensation depth, profiling response delay, and natural variation in terminal-bud morphology. Future work should focus on adaptive compensation, faster profiling response, lighter mechanisms, optimized rubber materials, and multi-variety field validation to improve topping accuracy and operational stability.