Color space is the basis of color image processing. Under normal circumstances, there are two kinds of color description: RGB color space and YCbCr color space. In the video process, normally the obtained and displayed colors are described by RGB. YCbCr color space is introduced to reduce the bandwidth and information storage. Selection of color space directly affect treatment methods and results. This paper introduces the conversion between the two color space, given the conversion equation. And the conversion is realized by Verilog language and verified through FPGA, the correct result is gained.