The utility model discloses a mechanical arm grabbing mechanism which comprises an external connecting plate, an adjusting mechanism is arranged on the external connecting plate, the adjusting mechanism comprises a rotating shaft, a fixing sleeve, a spring, an inserting sleeve, an inserting rod, a fixing mechanism, an abutting head, a telescopic mechanism, a vertical rod and a fixing plate, the rotating shaft is installed on the side wall of the fixing sleeve, the rotating shaft is rotationally connected to the external connecting plate, and the spring is arranged on the spring. The spring is installed on the fixing sleeve, the fixing mechanism is connected to the fixing sleeve and the inserting rod in a matched mode, the adjusting mechanism can dynamically adjust the elastic force and flexibility of the spring according to the requirement of a grabbing task, accurate grabbing force control is achieved, the adjusting mechanism can provide proper supporting and adjusting in the adjusting process through the arrangement of the inserting rod, and the grabbing force is adjusted. Therefore, the flexibility and the accuracy of adjustment are improved.