In order to have a higher reliability, accuracy and stability in flow field test for 2D Particle Image Velocimetry (PIV) system, the CCD camera displacement adjusting mechanism was designed, according to the PIV system requirements and the function of flow field test working environment, then the structural design thought, composition, and capable functions achieved and its characteristics were expounded. Through the use of the mechanism for the flow field test, the result shows that using of the CCD camera displacement adjusting mechanism, can very well satisfy the job needs of PIV system in flow field test, while makes the whole system more simple, stable and efficient, and further makes flow field test results more reliable and accurate.