The invention discloses a minimally invasive robot mechanical arm having a large movement space and a high structural rigidity, which comprises a telescopic seat provided with a surgical tool, wherein one end of a connecting rod IV is connected with the telescopic seat, a connecting rod V and a connecting rod VI are arranged at both sides below the connecting rod IV, one end of the connecting rod V and one end of the connecting rod VI are connected with the telescopic seat, the other end of the connecting rod IV is connected with the top end of a connecting rod I, the other end of the connecting rod V and the other end of the connecting rod VI are connected to outer walls at both sides of the top part of the connecting rod I, the bottom end of the connecting rod I is connected with the front end of a joint II seat, the bottom end of a connecting rod II and the bottom end of a connecting rod III are installed on outer walls at both sides of the back end of the joint II seat by rotating shafts, and the top end of the connecting rod II and the top end of the connecting rod III are respectively connected to the connecting rod V and the connecting rod VI; and the rotating shafts are connected with a second rotation driving device, and a connecting frame is connected with a first rotation driving device. By using the structure, the movement space of the mechanism is greatly enlarged, and the rigidity of the mechanism is increased, thereby lowering the requirements for the initial pose of the robot.