The invention discloses a high-precision three-dimensional soil pressure test device and a range adjustment system thereof. The device comprises a vertical main dynamometer spring, multiple horizontal dynamometer springs, a bottom plate, an inner cylinder, a central top plate, a side top plate and multiple outer side plates. The device is an inner-outer cylinder system, the inner cylinder is used for measuring vertical soil pressure and soil displacement, and an outer cylinder is used for measuring horizontal soil pressure and soil displacement of surrounding soil. The range adjustment system makes a conductor inside the dynamometer springs generate a magnetic field by electrifying the dynamometer springs, magnetic field force is controlled by controlling the magnitude of a current, stiffness of a dynamometer system is regulated, a range of the test device is controlled, and thus soil pressure real-time monitoring of ultra deep foundation pit soil, excavation soil close to a bridge pier and ultra high side slope internal soil is achieved.