Mechanical arm

The invention discloses a mechanical arm. The mechanical arm comprises a semicircular main connecting and fixing plate, a left semicircular clamping plate, a right semicircular clamping plate and a door catch type rapid clamp, wherein a cap type pipeline emergency maintenance fixture is grabbed through cooperation of the semicircular main connecting and fixing plate, the left semicircular clamping plate, the right semicircular clamping plate and the door catch type rapid clamp. The mechanical arm is simple in structure and corresponds to the cap type pipeline emergency maintenance fixture in a one-to-one mode, and therefore limiting, clamping and installation are facilitated; within the oil and gas leakage spreading range which emergency maintenance personnel cannot be close to, the cap type pipeline emergency maintenance fixture can be pre-installed manually so that repair welding can be conducted, and operation is safe and reliable; a control circuit or a hydraulic pipeline applied to the mechanical arm and