The shortcomings in current method of mean friction coefficient calculation of scuffing strength were analyzed.Based on the meshing characteristics of gear drive with meshing beyond pitch point and the formula of involute cylindrical gear in related standard

a more reasonable and accurate calculation method of mean friction coefficient was proposed to meet the need for calculation of scuffing strength of the gear drive with meshing beyond pitch point.Through calculating the examples of external-meshing and internal-meshing gear drive with meshing behind and before pitch points

it was found that errors of mean friction coefficients are more than 18.5% except external-meshing gear drive with meshing before pitch point

when they are calculated by standard formula;all of errors are less than 6.5% when they are calculated by improved formula

which confirms that the improved calculation method of mean friction coefficient is more accurate.This calculation method is also applicable to the normal transmission of gears.