The invention discloses a hydraulic mechanical arm suitable for cutter changing operation of a shield tunneling machine. The hydraulic mechanical arm comprises a base. The base is provided with a waist part. One side of the waist part is connected with one end of a big arm, and the other end of the big arm is connected with one end of a middle arm. The big arm is provided with a first hydraulic cylinder and a second hydraulic cylinder which are in pivot joint. The other end of the middle arm is connected with one end of a front arm. A third hydraulic cylinder is installed on the middle arm. A tool installing head is connected to the other end of the front arm. The front arm is provided with a fourth hydraulic cylinder. A hobbing cutter grabbing tool is arranged on one side of the tool installing head and comprises a U-shaped base. Two symmetrically-arranged grabbing tongs are arranged on a cross beam of the U-shaped base. One end of a fifth hydraulic cylinder is in pivot joint to the side wall of the U-shaped base, and the other end of the fifth hydraulic cylinder is in pivot joint with the grabbing tongs. All parts of the mechanical arm are hydraulically driven, super-high load capability is achieved, and a hobbing cutter of the shield tunneling machine can be easily grabbed. The hydraulic mechanical arm is simple and compact in structure, small in size, flexible in movement and capable of meeting the requirement for the cutter changing operation space. The digital hydraulic technology is adopted, and convenient and reliable control can be achieved.