The utility model provides a height measuring tool for a half flange of H-shaped steel of a forklift mast, which comprises the components of: a first reference block which is provided with a first reference plane; a first measuring block which is arranged at one side of the first reference block and is connected with the first reference block, and furthermore the first measuring block is provided with a first measuring plane and the distance between the first measuring plane and the first reference plane is an upper limit value of the height of the half flange of the H-shaped steel of the mast; a second reference block which is provided with a second reference plane; and a second measuring block which is arranged at one side of the second reference block and is connected with the second reference block, wherein the second measuring block is provided with a second measuring plane, and the distance between the second measuring plane and the second reference plane is a lower limit value of the height of the half flange. According to the height measuring tool, the first reference plane and the second reference plane are placed on a web of the H-shaped steel and then the measuring tool is horizontally moved in measurement, and the height of the half flange of the H-shaped steel of the mast can be quickly measured, thereby shortening measuring time, reducing measuring error and furthermore improving measurement accuracy and production efficiency of the forklift mast.