1. A method for removing background of a video, comprising: receiving the video from a storage device; retrieving a plurality of frames from the video, every frame is buffered in a memory of a computer system; analyzing an image feature of each frame, and acquiring correlation between adjacent pixels in each frame; forming multiple color blocks based on the image feature of each frame, wherein identification data associated with every color block is stored in the memory; the pixel values are saved to the memory, and every pixel is associated with a corresponding color block having its unique identification data; computing a difference of the pixel values within every color block between a preceding frame and a following frame to obtain a variance for each color block; in response to the variance of the color blocks between the preceding frame and the following frame, determining a target object including one or more connected color blocks; for every frame, the identification data of the one or more color blocks covered by the target object are jointly saved to the memory; and setting the color blocks other than the color blocks covered by the target object to be transparent blocks.