More and more attention has been paid to the lighting sources with intelligent dimming according to the psychological and physiological states of people.To rea lize accurate dimming of light-emitting diode (LED),this paper deduces a functional relationship betw een chromaticity coordinate and three channels′ duty,according to gravity principle and the characteristics of pulse width modulation (PWM) dimming, where the luminous flux is proportional to the duty cycle.This functional r elationship has been verified by light mixing experiments with red green blue(R /G/B),red green cold white(R/G/CW)、warm white green blue(WW/G/B) LED modules,and the dimming effects with effici ency of light,color rendering index and maximum luminous flux are evaluated.The results show that th is model with the advantage of high precision can be applied to various types of LED dimming colors,the deviation of chromaticity coordinate is less than 0.002between the set value and the measured value,and the deviati on of color temperature is less than 50K.Using cold white or warm white LED with plentiful spectra instead of blue and green LEDs in R/G/B module is conducive to improve the color rendering index of mixed light.It is o bserved that WW/G/B LED module has the best dimming effect.