A source driving method and a source driver for a liquid crystal display device having a plurality of pixels, wherein each pixel comprises a first color sub-pixel with a first displaying wavelength, a second color sub-pixel with a second displaying wavelength less than the first displaying wavelength, and a third color sub-pixel with a third displaying wavelength less than the second displaying wavelength are provided. First, a digital data is received. Then, a digital to analog process is performed to convert the digital data into an analog data. Next, the analog data is sequentially selected and output to the first color sub-pixel, the second color sub-pixel, and then the third color sub-pixel of the selected pixel. The source driving method can improve the image color fidelity of the liquid crystal display device.