The invention relates to a geomechanical model test device adopting a self-balancing double-loading mode and a test method. The geomechanical model test device comprises a force bearing rack, a base plate, a bottom plate, a counter-force plate, a gravity balancing weight, bolts, an isolation plate, a hydraulic jack, a hydraulic workstation and a servo controller. The force bearing rack is formed by welding rectangular square steel, the rigidity requirement of the device is met, and meanwhile the isolation plate is convenient to install and place. The base plate is located above a test body andbelow the jack (balancing weight), and therefore it is guaranteed that loads are evenly transmitted to the test body in the test process. Connecting holes are reserved in the force bearing rack and the counter-force plate, and the force bearing rack and the counter-force plate are spliced through the bolts, so that the requirements of tests on different loading modes are met. The device is simplein structure and reusable, migration of an experimental device can be realized without position limitation, and the device can realize quick and accurate loading and can also realize a long-term stable loading and unloading mode.