The present invention relates to a data driving system and method for driving a panel. The data driving system comprises: a gamma voltage supply and a D/A converter. The gamma voltage supply produces a plurality of gamma voltages. The D/A converter receives the gamma voltages, a first pixel value and a second pixel value, and converts the first pixel value and the second pixel value to a corresponding gamma voltage in the gamma voltages. When the D/A converter converts the first pixel value, the gamma voltages have a first polarity offset. When the D/A converter converts the second pixel value, the gamma voltages have a second polarity offset. Because the data driving system of the invention periodically switches the first polarity offset and the second polarity offset of the gamma voltage supply, an offset in the driving voltage is eliminated by the first polarity (positive) offset and the second polarity (negative) offset in space and time. Therefore, there is no band mura in the panel.