Abstract: Objective To discuss the efficacy of microsurgical approaches of small-bone-window posterior fossa decompression and cisterna magna angioplasty with conserved posterior arch of atlas in treatment of chiari malformation typeⅠ. Methods Twentythree cases with arcus posterior atlantis in the treatment of CMI in Chinese PLA General Hospital from March 2013 to June 2014 were selected. Patients had undergone small-window posterior fossa decompression and cisterna magna angioplasty with conserved posterior arch of atlas through posterior midline approach （from 2 cm under inion to 5 cm on C2 spinous processes）， and the cisterna magna was reconstructed， the cerebellar tonsil subpial was resected， and duraplasty was performed. The long-term efficacy was observed for 1 week and 3 months postoperatively， and KPS score was used to evaluate the conditions after operation. Results One week after operation， the neurological condition was improved in 19 cases， while 4 cases had no change. The average KPS score increased from （53.5±9.8） preoperatively to （66.52±9.8） postoperatively （P＜ 0.00）. And 3 months after operation， 6 cases were cured， 3 cases were relieved， 1 case had no change and 1 case was exacerbation， which was better than 1 week postoperative condition （P＜ 0.03）. The average KPS score of 3 months after operation increased to 85.2±14.7 （P＜ 0.00）. Cerebellar tonsillar hernia and syringomyelia shrank or disappeared obviously within 2-year follow-up. Conclusion The microsurgical approaches of small-window posterior fossa decompression and cistern magna angioplasty with conserved posterior arch of atlas shows excellent efficacy and less complication in treating chiari malformation typeⅠ.