Abstract： Objective To evaluate the shaping ability of two nickel-titanium rotary systems(ProTaper and Hero642)in simulated S-shaped canals.Methods Thirty simulated S-shaped canals were randomly divided into three groups and prepared by ProTaper,Hero642,ProTaper combined with Hero642 respectively.All the canals were scanned before and after instrumentation,and the amount of material removed in the inner and outer wall and the canal width after instrumentation were measured with a computer image analysis program.Results There was significant difference in the amount of material removed at the inner side of apical curvature and outer side of apex between ProTaper combined with Hero642 and ProTaper files ( P＜0.05)at the same tip size.The inner and outer wall of the canals were evenly prepared by ProTaper combined with Hero642,and the taper of canals were better than those prepared by Hero642.Conclusions ProTaper combined with Hero 642 had better shaping ability to maintain the original shape and could create good taper canals in the simulated S-shaped canal model.