The invention discloses a large-scale soil interface shear test model and a test method. The test model consists of a model box, test materials, pressurization equipment, shearing equipment and measuring equipment. The model box comprises an upper box and a lower box, the test materials include sandy soil and clay, the pressurization equipment includes a pressure plate, an upper pressure plate, a pressure spring fixed column, a pressure spring, a double-end stud and a bottom plate, the shearing equipment consists of a left baffle plate, a fine thread screw and a handle, and the measuring equipment comprises a right baffle plate, a pressure sensor, a vertical displacement sensor, a horizontal displacement sensor and a camera. The test method comprises the steps of: determining the test materials, consolidating lower box soil, performing soil interface treatment, and carrying out shearing model test. The large-scale soil interface shear test model and the test method provided by the invention can be used for studying interface shear strength change rule and soil shear deformation rule generated due to interfacial effect among different soil layers. Different from other large-scale direct shear equipment with high cost and complex procedures, the test model provided by the invention has the advantages of direct and simple design, rich source materials, and low cost.