Objective:To study the different modus operandi of posterior fossa decompression on function recovery of spine cord in patients with Chiari malformation and syringomyelia.Methods:Of 87 patients with Chiari malformation and syringomyelia

51 patients were selected and big craniectomy was performed in all cases.The effects of big craniectomy in 51 patients and mini craniectomy in 36 patients were compared.Results:Among the 51 patients

22 patients(43.1%) improved significanly in their clinical symptoms

10 cases were stabilized

and 5 cases deteriorated.Among the 36 patients

28 patients(77.8%) improved significanly in their clinical symptoms

and 3 cases were stabilized.Conclusion:Surgical treatment may fully ameliorate the clinical syndromes.Mini craniectomy and expansile reconstruction of posterior fossa is a preferred surgery for the treatment of ChiariⅠmalformation.