Abstract: The uneven distribution of flow velocity in the sound transmission area distorts the ultrasonic signal propagation path, which in turn affects the accuracy of the ultrasonic gas meter. In order to solve the problem of low flow measurement accuracy caused by flow velocity disorder in the measurement pipeline in complex environments, a rectangular flow channel structure for an ultrasonic gas meter is designed in this paper. Combined with SpaceClaim software, a rectangular flow channel structure with three rectifiers was designed, and the designed rectangular flow channel was numerically simulated using Fluent software. Through theoretical analysis and numerical simulation results, it can be seen that the structure effectively solves the problems of flow velocity distribution disorder and low gas flow in the pipeline. Finally, the performance test of the ultrasonic gas meter was completed using the bell type gas flow calibration device. According to the calibration results, the ultrasonic gas meter prototype composed of this flow channel meets the requirements of the national 1.5 accuracy index within the flow range of 0.025 m³/h~4 m³/h, which verifies the effectiveness of the rectangular flow channel design in this paper.