Video frame-rate up-conversion is one of the common video tampering technologies in the time domain, which achieves the frame conversion of video from a low frame-rate to a higher frame-rate by periodically inserting intermediate frames between two frames in the original video. A detection algorithm based on the periodic properties of optical flow for video frame-rate up-conversion tampering is proposed in this paper. Firstly, the video is converted into images. Then the Horn-Schunck optical flow method is used to calculate the optical flow vector of each pixel in each frame, and the optical flow change rate of the adjacent frames is calculate. Finally, the fast Fourier transform is used for the spectral analysis of the optical flow change rate. And whether the inspected video is altered by frame-rate up-conversion would be determined by judging whether the ratio of the max spectrum amplitude and the mean spectrum amplitude is higher than a certain threshold. Experiment results show that the proposed algorithm not only can accurately identify the video tampered by frame-rate up-conversion, but also improve the robust performance of video compression well, and has certain practical application.