A self-built device for measuring the angular velocity of falling object in the process of free falling is introduced, and the influence of rotation error caused by different angular velocities of falling object on gravity measurement is evaluated. Aiming at the free-falling motion model of a falling object with an initial rotation speed in a vacuum cavity, the device adopts the principle of optical lever and uses a high-precision position sensitive detector (PSD) as a light tracking device to study and deduce the relationship between the reflected light displacement caused by rotation and the falling time. Then, the time displacement curve recorded by PSD is fitted to solve the rotation angular velocity of the single fall of the falling object. After adjusting the verticality of the vacuum cavity, the maximum rotational angular velocity value can be reduced to 16.88 mrad/s, the introduced gravity measurement uncertainty is 0.57 μGal, indicating that the falling object is released more stably at this state. The experimental results show that the device can not only further improve the installation and adjustment accuracy of the falling object transmission structure in the absolute gravimeter, but also monitor the attitude of the falling object in the working process of the optical interference absolute gravimeter, and further reduce the measurement uncertainty introduced by the falling object rotation.