In order to solve the problem that the tank antiaircraft machine gun can not exert its maximum power because of its short range when shooting at some air targets after 500 m range correction, uses the vacuum external ballistic equation. This paper deduces the relationship between the firing oblique distance and the elevation angle of the anti-aircraft machine gun when firing at the air target, and obtains the oblique distance of the anti-aircraft machine gun when firing at the air target at different elevation angles after correction at the distance of 500m, and analyzes the deficiency of the air-firing of the anti-air machine gun after correction at the distance of 500m. The viewpoint of adopting 700m range correction in general and 800m range correction when mainly shooting enemy helicopters is put forward. The live firing results show that the correction distance can significantly improve the air firing hit probability of tank anti-aircraft machine gun and give full play to its air firing effectiveness.