The present invention provides an image data sensing system comprising a controller and at least one image sensor connected in series. The controller comprises a control input port and a control output port. The controller transmits a command signal or a synchronizing signal to all image sensors via the control output port, and the image sensor transmits image data to the controller via the control input port. By this way, the number for the ports of the controller can be decreased. The present invention further provides a mechanism that the image sensor can operate at different timings if a number of the image sensor is more than one. The present invention also provides relative image sensing methods.