Combined diesel and gas gear system often works under heavy load, high speed, impact and other complex conditions. Tooth fracture can significantly affect the meshing quality of marine gear pair. Existing research mainly focused on characteristics of gear pair meshing stiffness based on given angle and number of broken teeth, the results of which showed a large deviation from the meshing stiffness in the actual form of broken teeth. To develop a computational method for gear pair meshing stiffness at any breaking angle, the broken teeth were divided into two forms, i.e. those parallel to the line of contact and those not parallel to the line of contact; their respective computing formula of the length of the line of contact of the gear pair at any broken angle was then derived, and the meshing stiffness of helical gear pair at any broken angle solved based on ISO stiffness calculation criteria. According to the results, when the broken teeth were parallel to the line of contact, as the length of the teeth increased, the time and severity of the impact on meshing stiffness both increased; after passing the broken teeth area, the stiffness would instantly return to normal. When the broken teeth were not parallel to the line of contact, within the broken teeth area, the single tooth meshing stiffness was zero, and general meshing stiffness reduced; when entering the non-broken teeth area from the broken teeth area, both the single tooth and general stiffness would gradually return to normal.