For the overall superficial velocity measurement of oil-water two-phase flow in horizontal pipeline, using Continuous Wave Ultrasonic Doppler (CWUD) technique, a calculation model considering the influence of holdup distribution is proposed. A CWUD system is composed of a pair of piezoelectric ceramic ultrasonic transducers with center frequency of 1MHz. According to Doppler Effect, the frequency difference between the transmitted and the received sound wave is proportional to the velocity of droplets. Due to the influence of holdup distribution and the velocity profile on the droplets' velocity and position, which affects the power spectrum, the flow velocity obtained by CWUD system is not the overall superficial velocity. On the assumption that the holdup distribution satisfies Gauss distribution, establish the modified Doppler power spectrum model. The influence of the mean and variance of the holdup distribution on the Doppler power spectrum is studied. Then the form of the model of calculating overall superficial velocity is determined. Based on experiments, the parameters of the model are determined respectively under different continuous phases. The experimental results show that the overall superficial flow velocity calculated by the model is in good agreement with the actual flow velocity. The relative error is less than 5.79%.