The invention discloses a method and a device for converting a plane video to a three-dimensional video, belonging to the technical field of computer multimedia. The method comprises the following steps: C1: reading a current frame; C2: if the read current frame is a key frame, cutting colors of an image of the current frame, and assigning a depth value of the cut image to obtain a depth map of the current frame; and if the read current frame is a non-key frame, obtaining the depth map of the current frame; C 3: obtaining a frame of the three-dimensional video on the basis of the rendering ofthe depth map according to the obtained depth map of the current frame; C4: continuously reading a next frame of the current frame, and returning to perform the steps C2-C3 till the three-dimensionalvideo is obtained. The invention can fully and automatically obtain the depth map corresponding to each frame image of one video sequence and better complete a task of converting the plane video intothe three-dimensional video.