An analytical model of vertex’s shear strain and shear strain rate was developed based on the process of serrated chip formation with geometry shape of serrated chip as a trapezoid. The chip deformations under different cutting speeds for GH4169 were discussed with the proposed model. The results showed that with the cutting speed increasing, the degree of chip deformation increased. The maximums of strain and strain rate were respectively 4.91 and 4.59×106s-1 with applied cutting speed range in 200~1000m/min.