A method and device for monitoring video signal transmission includes a signal encoding and transmitting module and the signal receiving module. The signal encoding and transmitting module receives a composite video signal from a video signal source to cut off a horizontal video data series following a predetermined horizontal synchronization signal following a predetermined vertical synchronization signal and add an identification code. The signal receiving module receives the composite video signal carrying the identification code and compares the identification code to transmit the composite video signal out when the identification code is correct.