The invention discloses a signal control method, which is suitable for display image of an update panel. The signal control method comprises steps that the display image is updated by using first image data; whether second image data is received is determined; when the second image data is not received, internal signals are generated selectively; the internal signals are used to enable a shift register, and the process return to the first step of updating the display image by using the first image data. When starting signals and the second image data are received, the starting signal are used to enable a plurality of shift register units of the shift register, and then a plurality of grid electrode signal lines of the panel are sequentially enabled, and the display image is updated by the second image data.