The utility model discloses a mechanical arm capable of automatically grabbing and holding an oil fence floating barrel. The mechanical arm comprises a mechanical arm connecting arm, an upper arm, a lower arm, an upper hook, a lower hook, a hook linkage rod and a hook oil cylinder. The upper arm and the lower arm are fixed to the mechanical arm connecting arm. The two ends of the hook oil cylinder are connected to the upper arm and the upper hook respectively. The upper hook is connected with the lower hook through the hook linkage rod. The upper hook and the lower hook are in linkage and act at the same time. A piston rod of the hook oil cylinder drives the hooks to do corresponding actions through telescopic actions so that the floating barrel can be grabbed and held. The upper hook and the lower hook are in linkage, the upper hook and the lower hook grab and hold the floating barrel at the same time, the structure of the mechanical arm is simplified, and fixing stability of the floating barrel is improved. The linear movement of the piston rod of the hydraulic cylinder is changed into the mode that the hooks rotate around the hook linkage rod through the hook oil cylinder, and the flexibility that the mechanical arm grabs and holds the floating barrel is improved.