The present disclosure discloses an image conversion method for converting RGB signal to RGBW signal and an apparatus thereof. A substitution rate of a W luminance output value of respective pixels in each frame is determined according to RGB luminance input values of the respective pixels in each frame, and accumulated proportions of RGB luminance output values and the W luminance output value in RGBW luminance output values of the respective pixels within a preset time before each frame. The RGBW luminance output values of the respective pixels in each frame is determined according to the determined substitution rate of the W luminance output value and the RGB luminance input values of the respective pixels in each frame. In this way, the RGBW luminance output values of the respective pixels in the present frame can be adjusted according to a utilization rate of respective sub-pixels in the respective pixels within a period of time before each frame, so as to substantially maintain working lives of the respective sub-pixels in the respective pixels uniform as far as possible, and to further improve a service life of an entire display.