The invention relates to a large-size freely combined model test device for a high ground stress underground engineering, and the device provided by the invention comprises a plurality of split mounting type counter-force jack horse devices, wherein the whole test device has a narrower upper part and a wider lower part; the side face of the whole test device is a slope; each split mounting type counter-force jack horse device comprises a top beam, a side beam and a bottom beam; flanges and high-strength bolts are used for connecting the top beam to the side beam and connecting the side beam to the bottom beam; the counter-force jack horse devices can be connected mutually or be connected to front and back counter-force beams; the upper parts of the front and back counter-force beams are connected to left and right pulling rods while the lower parts of the front and back counter-force beams are connected to a model lifting translation trailer system on the bottom beam; the top beam andthe side beam are both provided with hydraulic loading systems; and the baseboard of the device is provided with an automatic hydraulic model lifting translation trailer system, thereby being convenient and stable to move a test model in and out. The test device is flexibly assembled, is simply operated, can be used for conveniently loading and observing, is provided with the model lifting translation trailer system, and can be applied to the plane and three-dimensional geo-mechanical model test for the geotechnical engineering under the high ground stress condition.