In order to solve the problem that the national standard cannot accurately calculate the bending stress of cylindrical helical gear with variable pressure Angle hob, a modified algorithm for calculating the bending stress of gear with variable pressure angle hob was proposed. An imaginary hob is introduced to meshing an equivalent spur gear, the equation of gear root transition curve is established based on conjugate meshing conditions, and the calculation method of curvature radius of any point of tooth root was given according to Euler-Savary formula. Combined with GB/T 3480—1997, the tooth profile coefficient and stress correction coefficient of gear processed with variable pressure Angle hob were calculated, and the bending stress correction value of tooth root was obtained. Then, Kisssoft/Romax analytical solution, finite element numerical solution values were used to verify the rationality of the tooth root bending stress correction algorithm. The results show that the tooth root bending stress correction algorithm can accurately calculate the tooth root bending stress based on variable pressure Angle hob machining gear; the tooth root bending stress correction algorithm can make up for the defect that using GB/T 3480—1997 cannot calculate the tooth root bending stress of cylindrical helical gear processed by variable pressure Angle hob, so as to realize the seamless connection between gear strength design and actual processing and solve the problem of inconsistency between the calculation model and the real object.