Abstract: In the field of semiconductor manufacturing, the uniformity of the flow field in the IC equipment process chamber determines the quality of the coating. In this paper, a laser Doppler velocimeter (LDV) was used to measure the internal flow field of the vacuum chamber. Under different air intake and different chamber pressures, the distribution of the gas-velocity in each plane of the chamber was studied. The results show that the particle concentration and background noise are the two key factors that affect the measurement of gas-velocity in the chamber. Four methods are used to effectively reduce the interference of the background noise to the signal. Through a large number of experiments, the pressure range of the LDV to measure the gas-velocity of the chamber, as well as the relationship between the chamber pressure, the air intake and the gas-velocity is obtained. It verifies that the secondary homogenizer in the chamber has the function of uniform air distribution. The results provide data support for the design of IC equipment.