A functional relationship between chromaticity coordinate and the duty cycle based on the RGBW color mixing equations and the pulse width modulation drive (PWM) is deduced. Multi-constraint optimization simulation of the luminous efficacy of source (LES) and color rendering index of the mixed-light is carried out on a Matlab program, which is further verified by the experiments. The results show that the RGBW light source can produce a wide range of color temperature from 2703 K to 7692 K. Under the highest Ra achievable, the Ra reaches 95, while the LES can reach 108 lm/W under the condition of an optimized LES. Furthermore, by reducing the color rendering index, the luminous efficiency improves significantly. The color rendering index likewise increases by reducing the luminous efficiency. By balancing these two factors, it has found that RGBW light source with high LES and Ra over 90 can best satisfy the demand of the current lighting manufacturing.