The invention provides a minimally-invasive surgery assistant robot, relates to the field of surgery robots, particularly relates to a minimally-invasive surgery assistant robot and aims to solve the problem that an existing robot hardly opens high-quality and high-accuracy wounds in minimally-invasive surgery. The robot comprises a main shaft lifting mechanism, a main shaft rotating mechanism and a main shaft tail end opening and closing mechanism, wherein the main shaft lifting mechanism is used for driving a ball screw-nut pair via a coupler by using a motor, so that a movable plate exerts the lifting function on a guide rail pair; the main shaft rotating mechanism is used for transmitting torque to a long sleeve by driving two pairs of gears via the motor, then transmitting the torque to a main shaft and enabling the main shaft to rotate; the main shaft tail end opening and closing mechanism is used for transmitting the torque via a worm and gear and a pair of gears by using the motor, lifting a turntable and stretching an inner rod so as to close a tail end surgical instrument.