The invention provides a method for detecting a video monitoring system and a device thereof; a standard definition television test signal and a high definition television test signal are generated by a signal source generator; the test signals are accessed in a video channel of a video monitoring system to be detected, and with a video index of the video monitoring system to be detected, video data is collected, analyzed and tested by an automatic analyzer based on the control of a single board computer of a computer; and the test result is displayed in the form of graphic and data. The invention can more scientifically and objectively assess the signal index of digital television video equipment, can carry out the test on video indexes of random signal-to-noise ratio, synchronization amplitude, white strip amplitude, luminance nonlinearity, amplitude frequency characteristic and the like of the video monitoring system, simultaneously has the function of image display of the video to be detected, can generate gray scale signals of 11 grade, and meets the detecting requirement of the field of video monitoring; furthermore, the invention has simple structure, convenient use, lower detecting cost, and is applicable to on-site detection and fill the emptiness of special detection instrument in the detection field of domestic and foreign video monitoring project.