A video signal output system includes a first video chip and a second video chip. The first video chip includes a first video signal output circuit and a simulation signal generating circuit. The simulation signal generating circuit outputs a first simulation signal and a second simulation signal. The second video chip includes a second video signal output circuit. The first video signal output circuit generates a first horizontal synchronization signal according to the first simulation signal, and generates a first vertical synchronization signal according to the second simulation signal. The second video signal output circuit generates a second horizontal synchronization signal according to the first simulation signal, and generates a second vertical synchronization signal according to the second simulation signal.