A source driver includes a first drive channel circuit, a voltage controller and a first programmable voltage buffer unit. The first drive channel circuit receives a first pixel data from the timing controller via a data bus, converts the first pixel data to a first drive voltage according to a first reference voltage group, and drives a display panel by the first drive voltage. The voltage controller receives a voltage command from the timing controller, generates and changes a first reference voltage configuration data according to the voltage command. The first programmable voltage buffer unit is coupled to the voltage controller and the first drive channel circuit, and receives the first reference voltage configuration data to generate and adjust the first reference voltage group for applying to the first drive channel circuit. Furthermore, a method for updating a new gamma curve by the source driver is also provided.