Abstract: Objective To observe the clinical efficacy of preparation of primary molars root canals with Protaper hand ni-ti file. Methods Select dental outpatients aged 4-8 years old who visited our department between 2010.1-2012.2, 160 primary molars which needed root canal treatment were randomly divided into two groups. 80 of them were prepared with Protaper hand ni-ti file crown-down the root, and the other 80 teeth were prepared with stainless steel K-file step by retreating preparation of the root canals. Metapex paste was injected into root canals, and immediately films were taken to evaluate the success rates of root canals. Assess pain rates in the return visit three days after the treatment. Results Pain rate of Protaper group was 3.75%, while pain rate of stainless steel K-file group was 15%, p <0.05, and there was significant difference. Success rate of the Protaper group was 95% , while success rate of stainless steel K-file group was 83.75% , p <0.05, and there was significant difference. Conclusion It is fast and efficient to use Protaper hand NiTi file in preparation of primary molars. Its tube pain response is light, and Its clinical efficacy is better than that of hand stainless steel K-file. So it's worthy of promotion.