An over-constrained self-balancing three-degree-of-freedom parallel-connection platform comprises a base, a movable platform, a five-rod closed-loop kinematic chain and two drive branches of the same structure, wherein the five-rod closed-loop kinematic chain is composed of a linear actuator, two coaxial first rotary pairs, a triangular frame, a second rotary pair, a public shaft, a third rotary pair and a spring booster movable pair; the two drive branches are each composed of a linear actuator, a first universal hinge, a connection rod and a spherical hinge; the movable platform is connected with the two ends of the public shaft of the five-rod closed-loop kinematic chain through two coaxial fourth rotary pairs; and the spring booster movable pair is vertically installed in the center of the base. The over-constrained self-balancing three-degree-of-freedom parallel-connection platform is provided with a fixed decoupling rotary shaft, the torsional rigidity around the center line of the base is large, and the bearing capacity is high.