The invention discloses a carrying mechanical arm firm in clamping. The carrying mechanical arm comprises a rotation base. A first mechanical arm body is arranged on the rotation base. The end, away from the rotation base, of the first mechanical arm body is connected with a second mechanical arm body through an electric rotating shaft. A clamping mechanical jaw is arranged at the end, away from the first mechanical arm body, of the second mechanical arm body and comprises a beam. One side of the beam is fixedly connected with the second mechanical arm body, and bolt holes are formed in the other side of the beam in the center line in the length direction at equal intervals. Clamping connection rails are arranged on the two sides of the bolt holes correspondingly. Clamping arms are driven through first cylinders, the clamping strength is stable, the situation that because the clamping force is instable, carried goods fall cannot happen, bolts are inserted in the bolt holes through a second cylinder after the goods are clamped, the positions of the clamping arms are mechanically fixed, the clamping strength is kept unchanged, the aim of stably clamping the goods is achieved, and the goods carrying safety and efficiency are improved.