Abstract: Accurate measurement of irrigation canal flow is a crucial step in achieving efficient water resource utilization and scientific irrigation management. This study aims to address the issues of high cost and low measurement accuracy of traditional agricultural irrigation canal flow measurement devices by designing a box-type flowmeter based on the ultrasonic time difference method. Firstly, the mechanical structure of the box-type flowmeter was designed, and a staggered array layout method was proposed to effectively increase the number of channels. Secondly, a data acquisition circuit was designed to improve the time-to-digital converter (TDC) timing circuit by adding a boost drive circuit at the ultrasonic transmitter end and an ultrasonic echo signal conditioning circuit at the receiver end, thereby enhancing the measurement distance and the accuracy of echo signal arrival detection. A 16-channel shared timing circuit was implemented using analog switches to reduce circuit cost and increase system integration. Finally, in data processing, data correction and the introduction of the 53H improved algorithm and weighted data fusion improved algorithm were employed to achieve precise measurement of irrigation canal flow velocity. In the static water test, the nonlinearity of the data acquisition circuit channels, channel inconsistency, and ultrasonic transducer inconsistency were tested. Additionally, the influence of temperature on the measurement results was tested in the static water test. In the dynamic water test, the 53H improved algorithm was used to process the time difference data, and the improved weighted data fusion algorithm was used to solve the optimal weight coefficient of the flow velocity of each channel, the measurement results were compared with those of an electromagnetic flowmeter. The results showed that the maximum channel nonlinearity error was 0.95%; the channel inconsistency was 0.047 ± 0.0322 ns, resulting in a maximum flow velocity error of 3.06×10⁻⁴ m/s; the ultrasonic transducer inconsistency was 0.2882 ± 0.2152 ns, leading to a maximum flow velocity error of 2.50×10⁻³ m/s. These errors can be corrected through data correction methods. Within the range of 20 to 40 ℃, the root mean square error of the flow velocity was 1.70×10⁻⁴ m/s, and the influence of temperature on the measurement results could be ignored. In the dynamic water test, the deviation of the box-type flowmeter measurement relative to the electromagnetic flowmeter was 0.16% to 0.93%, achieving the same measurement accuracy as the electromagnetic flowmeter. The research results provide important technical support for the precise measurement of irrigation canal flow and the realization of efficient water-saving irrigation.