The invention discloses an outer wall building module and application thereof. The outer wall building module comprises an outer wall board, a steel frame, a heat-insulating layer and an inner wall board. The steel frame is composed of side frames and a steel keel, the side frames are arranged on upper, lower, left and right side faces of the building module, the steel keel connects the upper side frame with the lower side frame and is arranged perpendicularly, each side frame comprises Z-shaped steel and an H-shaped heat-insulating strip, two pieces of the Z-shaped steel are symmetrically embedded in the H-shaped heat-insulating strips, a U-shaped inserting connecting groove is formed in the middle, side wing frames are formed on two sides, a cavity in the steel frame is filled with a heat-insulating material to form the heat-insulating layer, and the inner wall board and the outer wall board are parallelly fixed in the side wing frames on two sides of the steel frame. The outer wall building module is high in heat insulativity and strength and can be in factorized mass production.