Abstract: A method of measuring ion drift velocity on the condition of high gas pressure was mentioned，and theoretic analysis was done. An experimental measurement system was also built. A DDC112 current integral amplifier was used to measure the output current pulse signal of ionization chamber filled with 4 MPa xenon by fixed integration time integral measurement and stepping integration time integral measurement. The quadratic curve and cubic curve were fitted by experimental data based on the theoretic analysis. The ion drift time was calculated by proportional relationships of curve coefficient. According to the structure and running conditions of ionization chamber, the xenon ion mobility in 4 MPa xenon was calculated and the value is 0.018 1-0.019 6 cm²•V^－1•s^－1. The xenon ion mobility in 0.1 MPa xenon was calculated by extrapolation method and the value falls within the interval 0.72-0.78 cm²•V^－1•s^－1，that is in good agreement with the data from literatures.