The invention discloses a screen splicing system and a video data stream processing method. The system includes: a video acquisition subsystem, configured to acquire an original video data stream, and output the acquired original video data stream to a smooth displaying subsystem after a smooth displaying image processing mode is enabled; the smooth displaying subsystem, connected with the video acquisition subsystem and configured to receive the original video data stream from the video acquisition subsystem, sequentially perform smooth displaying image processing and screen cutting processing on the original video data stream and send the cut video data stream to a screen splicing subsystem; and the screen splicing subsystem, connected with the smooth displaying subsystem and configured to perform splicing processing on the cut video data stream and send the spliced video data stream to a splicing display wall. According to the technical solutions provided by the invention, screen splicing display smoothness is improved, and an overall display effect of the screen splicing system is remarkably improved.