This paper addresses the issue of oil-water two-phase flow measurement under complex downhole conditions by developing an ultrasonic Doppler flow meter with sound velocity compensation. By establishing a one-dimensional velocity profile measurement model based on the Doppler effect and a sound velocity measurement model based on pulse echo intensity, and combining these with the principle of layered integration, a sound velocity compensated flow measurement model is constructed to achieve adaptive reconstruction of the velocity profile and high-precision flow measurement. On this basis, ultrasonic transducers and high-speed excitation and reception control boards suitable for high-temperature and high-pressure downhole environments are designed, and digital signal processing technology is used to achieve online demodulation of flow. Additionally, to ensure reliable operation under downhole high-temperature and high-pressure conditions, the measuring pipe section has been structurally and sealingly designed. A downhole flow test prototype has ultimately been developed. Experimental results indicate that the flow measurement module has a measurement error of less than 1% in the laboratory environment, can rapidly respond to fluid fluctuations, and can operate stably under extreme downhole conditions of 125℃ and 60 MPa. This technology can be widely applied to downhole measurement and adjustment scenarios and can be integrated into intelligent measurement and control systems, providing technical support for the construction of smart oil fields.