Aiming at the problems of color fading and chromaticity coordinate deviation in the existing railway signal in China, an idea of single lamp multi display light emitting diode (LED) mixed light intelligent signal is proposed in this paper. First, according to Grassmann's law and International Commission on illumination standard chromaticity system mixing principle, the RGB (Red, Green, Blue) three-color mixing modulation system is established. Then, the functional relationship between duty cycle, chromaticity coordinates and related color temperature is established, and the RGB three channel moon white, yellow and purple lights are adjusted by pulse width modulation. Finally, the design and construction of three channel mixed light modulation system with adjustable duty cycle are completed, and the simulation and experimental verification are carried out combined with the relative luminous flux attenuation data. The results show that the RGB three-color light system can accurately set the relevant chromaticity coordinates of each color light and realize the chromaticity adjustment under different conditions, so as to meet the needs of railway signal display.