Provided is a self-adaptive pneumatic flexible grabbing mechanical gripper based on a metamorphic mechanism. A support is fixedly connected with a base to form a frame-shaped structure, an air cylinder is located in the frame-shaped structure and is fixedly connected with the base, the gripper comprises a slider crank mechanism and the metamorphic mechanism, chunks are fixedly connected with the metamorphic mechanism, a workpiece is a grabbing object, and contact force sensors are arranged on the surfaces, making contact with the workpiece, of the chucks. Connecting rods are connected to an air cylinder piston through revolute pairs A, the connecting rods are movably connected with the metamorphic mechanism, and the slider crank mechanism is formed by the connecting rods, the air cylinder piston and connecting rods 1 in the metamorphic mechanism, the air cylinder piston is the slider of the slider crank mechanism, the connecting rods are movably connected with the air cylinder piston, and a force feedback control system is connected with the contact force sensors and the air cylinder. Compared with the prior art, the self-adaptive pneumatic flexible grabbing mechanical gripper based on the metamorphic mechanism achieves the purposes of being little in drive, simple in control, low in cost and high in reliability, having certain flexibility, and being capable of self-adaptively grabbing objects in complex space geometrical shapes or simulating the movement characteristics of human hands.