The invention discloses a cross arm and a power transmission pole. The cross arm comprises a hollow pipe, a wire hanging fitting and a lightning arrester core body, wherein the hollow pipe is arrangedto be of a hollow structure in the axial direction; the wire hanging fitting is positioned outside the hollow pipe, is connected with the hollow pipe and is used for hanging a power transmission line; and the lightning arrester core body is located in the hollow pipe and is insulated from the hollow pipe, the input end of the lightning arrester core body is electrically connected with the wire hanging fitting, and the output end of the lightning arrester core body is electrically connected with a grounding bracket. The cross arm provided by the invention has a lightning protection function, and is simple in structure and convenient to install.