Objective To investigate the application effects of Waveone Gold,Protaper,MTwo and Reciproc on curved root canals of molar teeth.Methods Collect 100 curved in vitro molars and randomly divide them into 5 groups,Root canal preparation was performed using Waveone Gold,Proteper,Reciproc,MTwo,and stainless steel K-files,respectively.Compare the root canal preparation effects and related complications,root canal offset,and root canal filling effects among five groups.Results After analysis,the five groups of root canal preparation time,the difference was statistically significant,Waveone Gold group the shortest preparation time(P<0.05).There were statistically significant differences in the incidence of step formation among the five groups(P<0.05),but there were no statistically significant differences in the incidence of lateral root canal puncture and instrument fracture among the five groups(P>0.05).The root canal offset of 2mm,4mm and 6mm vertical plane in the five groups was small,the difference was statistically significant,and the root canal offset of Waveone Gold group was the smallest(P<0.05).There was no statistically significant difference in overcharging rates among the five groups(P>0.05).However,there was a statistically significant difference in overcharging and underfilling rates among the five groups(P<0.05),with Waveone Gold and Reciproc groups having higher overcharging rates than the control group and lower underfilling rates than the control group(P<0.05).Conclusion The application of Ni-Ti instruments in curved molar root canals can shorten the preparation time of root canals,reduce the related complications,reduce the deviation of root canals,better root canal filling effect,especially Waveone Gold have obvious advantages.