Centroidal deviation is an important factor for projectile flight stability, and it is the key for accurate measurement to calculate ballistic trajectory. In order to solve fault about an equipment used to automatically measure centroidal deviation when it is used to test special shape of the projectile. Its accurate driving mechanism has some problems such as clamping stagnation and skid and etc. so. In the paper, according to its measurement principle and test procedures, the equipment deficiencies are analyzed, and the solutions such as improving supporting method and increasing the rotary torque with the deceleration servo motor are put forward, design and calculation are introduced in detailed. The test result shows that the improved mechanism can directly drive irregular projectile with motor, and the measurement accuracy can be improved about 4.15 times. Its measurement range is broaden and its measurement precision and efficiency are improved, so it has good application value.