In order to solve the problem of replacing TFT screens of different specifications when testing UHD video processing motherboards, and further shorten the test time, a system structure is proposed that combines the scale conversion and field frequency reduction of FPGA devices with DDR3 SDRAM memory chips to normalize video signals with different resolutions and field frequencies into HD video signals. The system uses 4 K@ 60 Hz UHD video as the input signal and sends it to the video data reading and writing module composed of DDR3 controlled by FPGA to realize cross-domain transmission, down-scale conversion processing and data connection; continuous output the HD video signal after down-scale conversion and field frequency reduction. After comparative experiments, compared with the storage structure of multi-channel FIFO plus DDR3, the storage resources consumed are reduced by 352 256 bits, and the conversion process time is reduced by 6. 761 μs. The results show that this system is more suitable for the testing requirements of video processing mainboards on production lines.