Abstract： Foramen magnum decompression is the shared procedure for Chiari type 1 malformation(CM1).There is no single and clear treatment method,and the scope of decompression and clinical efficacy are controversial.The improvement of cere-brospinal fluid hydrodynamics may be related with the relief of clinical symptoms.The combination of cine phase-contrast magnetic resonance imaging(PC-MRI)and intraoperative ultrasound(IOUS)can accurately assess the cerebrospinal fluid hydrodynamics chan-ges at the cranio-vertebral junction.The combination of these two can provide useful information for the assessment of the degree of damage,guide the selection of surgical methods,predict clinical improvement effect,and reduce reoperation rate.This article reviews the clinical application of PC-MRI combined with IOUS in the selection of CM1 surgical procedures.