A method of controlling color mixing of red, green, and blue LEDs based on photometry theory is presented. The (x, y) chromaticity coordinate can be acquired while the ratio of duty cycle signal is changed. It can achieve color mixing of RGB LEDs by pulse width modulation (PWM) control circuit sending duty cycle signal to LED driver. In this paper, the variations in chromaticity coordinates by controlling color mixing of red, green, and blue LEDs based on photometry theory will be discussed. From the experimental results, it is evident that the chromaticity coordinate variations Δuv of red, green, and blue LEDs are less than 0.0071, 0.0105, and 0.0110, respectively. Besides, A/D converters and microcontroller is used to implement the feedback control mechanism and the front panel of LabVIEW program is used for the development of the control algorithm. However, it is clear that the experimental results and the theoretical data are in good correspondence.