It is difficult to recognize microexpression because of its small range and short duration. To solve this problem, a micro expression recognition method based on 3D Convolutional neural network (C3D) and optical flow method is proposed. We first extract a series of optical flow images with dynamic features from the microexpression video by optical flow method, then input the obtained series of optical flow images with the original gray-scale image sequences into the C3D network, and then extract the features of micro expression in the time and space domain by C3D. Simulation experiments on the open data set CASMEⅡ show that the recognition accuracy of the proposed method is 67.53%, which is better than the existing methods.