The present invention is to provide an image output test system, which is built in between an image output device and an image output test device, in which the image output test device can receive a first video signal, convert the first video signal into a second video signal and further proceed sampling on the second video signal for acquiring a sampling result, and the image output device can output the first video signal through an image output terminal thereof, receive the sampling result from the image output test device, and compare the sampling result with a preset reference value to determine whether the image output terminal is good or not.