Flexible joint of assist robot

The invention belongs to the field of assist robots, and particularly discloses a flexible joint of an assist robot. A main motor is installed in a case of the assist robot. A middle connecting rod is connected to the output end of the main motor. A lead screw is installed on the middle connecting rod in a rotary mode. Any end of the lead screw is connected with the output end of an auxiliary motor installed on the middle connecting rod. The lead screw and the auxiliary motor are driven by the main motor to rotate along with the middle connecting rod. A spring sliding block set is connected to the lead screw. The auxiliary motor drives the lead screw to rotate, and drives the spring sliding block set to make linear reciprocating movement through the lead screw. Guide rods connected with the two ends of the spring sliding block set are arranged on the two sides of the lead screw respectively. The two ends of each guide rod are connected with a base plate through connecting rods respectively. The lead screw dri