The invention discloses a grabbing mechanical arm, and belongs to the field of machines. According to the technical scheme, the grabbing mechanical arm comprises a base, a supporting frame, a grabbingdevice and a stress application spring; a rotating tray is tightly attached to the upper portion of the base, the supporting frame is fixedly connected to the outer wall of the upper portion of the rotating tray, fixing blocks are fixedly connected to the two sides of the outer wall of the supporting frame, a vertical positioning shaft is in through connection with the middles of the fixing blocks, a hydraulic air cylinder is fixedly connected to the upper portion of the rotating tray, the upper portion of the hydraulic air cylinder is in through connection with a vertical telescopic shaft, the upper end of the vertical telescopic shaft is fixedly connected with a lifting rod, and the side, away from the supporting frame, of the lifting rod is in through connection with two transverse positioning shafts. Through the stress application spring, a clamping arm can shrink inwards, the effect of increasing the grabbing force of the clamping arm is achieved, the problem that due to too heavy workpieces, the workpieces are prone to slipping away from the clamping arm is solved, the grabbing quality of the clamping arm can be effectively improved, axial deviation of the clamping arm can be avoided, and structure stability of the mechanical arm is effectively improved.