The invention relates to a method of determining a power transmission line iron tower cross-arm wind load, which is realized through a wind tunnel test and comprises the steps of: (1) obtaining parameters; (2) determining a cross-arm wind load partition coefficient K theta in the wind of different angles; (3) determining a cross-arm wind load standard value Wsc when wind blows in a mode of being perpendicular to the front face of a cross-arm; and (4) determining a wind load standard value W theta of the cross-arm along a wind direction. The method considers the influence of wind in different angles, is not limited to four common angles of wind in the Technical Regulation of design for tower and pole structures of overhead transmission line, and has the characteristics of better applicability and higher precision.