Considering the problem that the high requirement of flow accuracy in special industry, whereas the traditional flow measurement method is difficult to achieve, the Ultrasonic Doppler Velocity Profiler (UVP) has been adopted to accurate flow measurement of pipeline fluids. According to the physical model of acoustic wave propagation in water-pipe wall-water three-layer medium, a mathematical model containing the product of frequency thickness (the product of detection frequency and the thickness of pipe wall), the transmission coefficient and the incidence angle is established. Optimizing Doppler incidence angle with transmission coefficient is a key measurement parameter. The simulation results show that the transmission coefficient is larger when the incident angle is at 45 to 55 degrees, moreover, the incident angle presents a periodic distribution in the range of 0° to 20°with high transmission coefficient. Taking plexiglass tube as the experimental object. The error between the flow rate measured by UVP method and the standard flow rate under different incident angles is studied, and the results show that minimum flow error at an incident angle of 10°.Combining simulation and experimental results, the optimal incident angle for measuring the flow rate by the UVP method is determined to be 10°. Comparing the flow calculated by the single-position velocity distribution with the flow calculated by multi-position velocity distribution interpolation in the circumferential direction, the former has a large error, the minimum is 1.417%, and the maximum is 8.97%; the latter error is 0.472%. The results provide a theoretical basis for accurate measurement of pipeline flow by ultrasonic Doppler method.