Large arm structure of multi-joint robot

The utility model discloses a big arm structure of a multi-joint robot. The big arm structure comprises a big arm body, a big arm cover plate and two dustproof assemblies. The big arm body comprises a big arm connecting rod, a first cavity and a second cavity; the big arm connecting rod is a hollow connecting rod with a hollow opening in the center of the upper part; one end of the big arm connecting rod is provided with a first cavity integrally formed with the big arm connecting rod and provided with an upper opening, and the other end of the big arm connecting rod is provided with a second cavity integrally formed with the big arm connecting rod and provided with an upper opening; the big arm cover plate is an arched shell cover; the large arm cover plate is detachably mounted above the hollow opening through a screw, and the area of the large arm cover plate projected to the large arm body can cover the whole hollow opening; the two dustproof assemblies are fixedly installed on the two sides of the large