The paper presents a design of compositing 6 channels of BT656 input video to one BT1120 output video undistorted by combining FPGA and video compositing system. Achieve the video data extraction,SRAM ping-pong operation and video splicing method by Verilog language. The video compositing system consists of video input decoding module,memory module,the output decoding module,I2C module and clock management module. After algorithm simulation and logic synthesis,the design can achieve the basic functions of video composition; meet the requirement of real-time video surveillance system. By the combined results we can know that this design occupied considerably less logic resources in the FPGA chip,and the entire design can run with very high frequency.