The invention provides a PWM light modulation method and device. A plurality of PWM periods are combined into a control signal, so as to achieve the control of the brightness of illumination equipment. After the above design is employed, the light modulation precision cannot be affected while the frequency of a PWM signal is improve. Through the change of a combined scheme, more light modulation levels can be obtained, thereby achieving higher light modulation precision and a more smooth and flexible light modulation effect.