The invention discloses a VOCs simulation test system and a VOCs concentration measurement method. The device comprises a system body, a VOCs adding device, an image acquisition device and a gas-phase VOCs detector; the VOCs adding device is arranged on the top of the system body, the image acquisition device is arranged at the side of the system body, and the gas-phase VOCs detector is connected with the system body; the system body is filled with an unsaturated soil layer, and a gas monitoring hole longitudinally formed in system body is connected with the gas-phase VOCs detector; the image acquisition device is used for acquiring frontal surface changes of liquid-phase VOCs, and the gas-phase VOCs detector is used for detecting the concentration, in the longitudinal direction of the system body, of gas-phase VOCs. According to the simulation test system for the VOCs in the unsaturated soil layer, the structure is reasonable, not only can changes of the liquid-phase VOCs frontal surface in the unsaturated soil layer be tested, but also concentration changes of the gas-phase VOCs and the liquid-phase VOCs in the unsaturated soil layer can be detected in real time, and practical significance on study of migration and concentration distribution rules of the liquid-phase VOCs and the gas-phase VOCs and correlation between the liquid-phase VOCs and the gas-phase VOCs is achieved.