Extension jib movable arm and engineering machinery

The utility model relates to engineering machinery, and discloses an extension jib boom and engineering machinery, including a plurality of cover plates, side plates, bottom plates and support members, the plurality of support members are connected through the plurality of side plates, the plurality of side plates are symmetrically arranged, the plurality of cover plates and the plurality of bottom plates are respectively and correspondingly arranged on the upper and lower sides of the side plates so as to enclose a box body structure with the side plates, and the height of the section of the side plate is greater than the width of the section of the cover plate. According to the movable arm of the extension arm, the supporting pieces are connected through the side plates, the cover plate and the bottom plate to form the box body structure, and the section heights of the front side plate, the middle side plate and the rear side plate of the movable arm are designed to be larger than the section width of the c