A method for increasing compatibility of DisplayPort includes: providing a first source device, a second source device, a controller, and a sink device, wherein the first source device is connected to the controller; the first source device transmitting a first image signal to the sink device via a main link for displaying the first image signal on the sink device; causing the controller to disconnect from the first source device and connect to the second source device; executing a simulation process to generate a DC level variation on an auxiliary channel between the controller and the sink device; the second source device transmitting auxiliary data to the sink device; the sink device transmitting link data back to the second source device; and the second source device transmitting a second image signal to the sink device via a second main link for displaying the second image signal on the sink device.