Self-balancing horizontal loading device for large test piece and test method

The invention discloses a self-balancing horizontal loading device and testing method for a large test piece, and the loading device comprises a counter-force beam which is fixed on the ground; the number of the to-be-tested pieces is two, and the two to-be-tested pieces are symmetrically installed on the counter-force beam; the jack is arranged between the two to-be-tested pieces, and the two ends of the jack are connected to the two to-be-tested pieces respectively; the monitoring sensing assembly comprises strain sensors, and the strain sensors are installed on the two pieces to be tested; wherein after being started, the jack can apply mutually separated acting force to the two to-be-tested pieces, and acting force and counter-acting force which are opposite in direction are generated between the two to-be-tested pieces. The two to-be-tested pieces are arranged at the same time, force is applied between the two to-be-tested pieces through the jack, so that the two to-be-tested pieces support each other, t