A source driver, an operation method thereof, and a flat panel display using the same are provided. The source driver includes a data channel, a switch and a switch controller. The data channel latches a pixel data according to timing of a line letch signal, and converts the latched pixel data to a driving signal for driving a display panel. The data channel decides a polarity of the driving signal according to a polarity signal. A first end of the switch is coupled to the data channel to receive the driving signal. The switch controller adjusts a pulse width of the line letch signal to obtain a control signal for controlling the switch according to the polarity signal. A pulse width of a first pulse is smaller than that of a second pulse in the control signal after the polarity signal is changed.