The disclosure provides a RGBW pixel rendering device, including a collecting module obtaining a RGB grayscale value, converters converting the RGB grayscale value to a RGB brightness value and converting a second RGBW brightness value to a RGBW grayscale value to be output, a sampler, converting the RGB brightness value to a first RGBW brightness value, a judging element obtaining saturation values and brightness values, and calculating the saturation values and the brightness values respectively to obtain a saturation value difference and a brightness value difference for judging, a rendering element rendering the first RGBW brightness value according to an outcome to obtain the second RGBW brightness values. The disclosure further provides a rendering method. Compared with the prior art, the display has relatively high resolution without losing details.