A clamping device of a mechanical arm comprises a first linear guide rail, a second linear guide rail, a movable block, a first clamping part, a second clamping part, two transmission rods and a driving mechanism. The clamping device of the mechanical arm has the advantages that by adoption of the scheme, the driving mechanism is capable of driving the movable block to reciprocate slidably along the first linear guide rail, the movable block drives the transmission rods to move synchronously, and the two transmission rods drive the first clamping part and the second clamping part to clamp and release through a first inclined slide groove and a second inclined slide groove respectively, so that a clamping function of the clamping device of the mechanical arm is realized, and structural simplicity and convenience in clamping are achieved; in addition, since the first inclined slide groove and the second inclined slide groove are symmetrical along a center line, clamping precision is constantly kept at the center line of the first inclined slide groove and the second inclined slide groove, and high clamping precision is achieved.