Abstract: The RV (rotate vector) reducer has been widely used in the joints of agricultural robots, due to its compact structure, high torque, and small transmission errors. However, it is often subjected to high duty and frequent load, leading to surface damage (such as scuffing of internal components) and a significant decrease in the load-carrying capacity. The present study aims to improve the load-carrying capacity of the RV reducer in complex field work environments. The problem of contact surface damage was also solved during crop planting and harvesting. The surface coating strengthening was applied to the cycloidal gear tooth surface. Tetrahedral amorphous carbon (ta-C) film was coated on the cycloid gear tooth surface using plasma-enhanced chemical vapor deposition (PECVD). A series analysis was then carried out. Firstly, a high-precision virtual prototype was constructed to identify the dangerous working positions and the maximum contact stress during cyclic transmission. The theoretical basis was provided for the fatigue performance and damage behavior testing. Secondly, the numerical analysis was conducted on the coexistence of rolling and sliding during transmission. The entire cycle was summarized to identify and then avoid the severe points of the sliding wear. The finding also provided a strong reference to select the work positions in practical situations. Finally, a high torque acceleration degradation test was conducted under different experimental conditions on the RV reducer comprehensive performance test bench. The RV reducer was disassembled to characterize the macroscopic wear of the key components. The microstructure and elemental distribution of the wear area after the test were observed using material characterization. The results showed that the maximum meshing force was generated when the meshing phase angle was equal to 46.19 º. The cycloid-pin pair showed that there was an outstanding linear contact and the contact stress, which increased from both sides to the middle to 346.13MPa. The ta-C coating significantly reduced the frictional stress of the tooth surface pairs. The contact stress of the outer ring of the needle-roller pair was greater than that of the inner ring. Once the meshing phase angle was equal to 180 º, the relative sliding speed reached the maximum of 0.18m/s. Furthermore, the pendulum pair exhibited pure sliding, particularly when the meshing phase angle was equal to 46.65 º. It implies that the present point was the position with the most severe sliding wear. The rolling speeds of the cycloid wheel and the needle wheel both approach 0 at the present position, indicating a trend of mutual restraint between rolling and sliding. The point around 46 ° was an extremely dangerous position in the transmission cycle. After coating modification, the efficiency reached 94.94% under rated conditions, with an increase of about 20%. Also, the root mean square (RMS) of the vibration signal and the periodic spikes were reduced with the smoother transmission. Severe fatigue wear occurred on the surface of the key components in the uncoated reducer, with the localized flaky peeling and pitting. The reducer exhibited the localized conventional fatigue wear. The oxidative wear was significantly reduced after coating modification. According to the experimental observation, the ta-C coating shared the anti-friction, anti-impact, and anti-oxidation properties, which significantly improved the overall load-carrying capacity of the RV reducer. The findings can provide important references to optimize the load-carrying capacity of the RV reducer in agricultural robots.