Based on NC machining, the tooth surface errors correction of spiral bevel gears was investigated. A new method for the machining settings transformation from cradle-type hypoid generator to Free-Form one was proposed, and the tooth errors mathematical model based on NC machining was established. The minimum of square sum of tooth surface errors was the objective function to optimize the cradle-type hypoid generator machine settings and transform those parameters into NC form so as to realize the NC machining correction of spiral bevel gears. Finally a numerical example was presented. The results showed that it could achieve precise correction after altering relative weight coefficient and optimizing for several times.