A source driver and an internal data transmission method are provided. The present invention employs specially designed switch units and creates specially designed data paths in a source driver, which matches with the driving method for dot invesion and the specially designed pixel array. When the dot inversion driving method is used on a pixel array of a specific design, each output buffer and digital-to-analog converter inside the source driver continuously output voltages of positive polarity and voltages of negative polarity, instead of switching between positive and negative polarities. Consequently, the swing voltages that the source driver outputs can be lowered, the power consumption can also be reduced accordingly, a smaller area is occupied, and the costs are reduced.