Abstract: Objective: To explore the effects of suboccipital decompression combined with occipital large pool reconstruction in the treatment of Arnold-Chiari typeⅠmalformation(ACM-Ⅰ) complicated with syringomyelia(SM) . Methods: Forty patients were treated with suboccipital decompression through posterior fossa small bone window, improving cerebralspinal fluid circulation and reconstructing occipital large pool under the microscope. results: After operation，MrI showed the cerebellar tonsil was above the level of foramen magnum and cisterna magna expanded. All patients were followed up for 3 to 30 months. No death case, the clinical symptoms improvement in 35 cases and no change in 5 cases were found, the effective rate was 87. 50%. Syringomyelia reduction in 33 cases and no change in 7 cases were found, the effective rate was 82. 50%. Conclusions: Suboccipital decompression combined with occipital large pool reconstruction is an effective way for treating ACM-Ⅰcomplicated with SM.