Objective: To compare the clinical characteristics of spinal muscular atrophy (SMA) in children within different phenotypes. Methods: Totally 66 cases were enrolled in this study .The comparisons were performed in clinical manifestation, changes of electrophysiology, genetic test of homozygous deletions of survival motor neuron 1 gene (SMN1) and follow-up study. The statistics analysis was done by SPSS software for Windows. Results: 63.3% of SMAⅠpatients were characterized by glossopharyngeal paralysis and 30.3% by paradoxical breathing, while the rate ratios were much higher in those with family history（80.0%,50.0%）of which the age onset were younger (1st month). For patients type Ⅱand type Ⅲ, muscle fibrillation and deformity were more common and functional abilities of some patients might improved naturally. EMG in 73.3% of the patients suggests a motor neuron disease. There was no difference between 3 groups, age factor excluded. Approximately 90.5％of the patients in our cohort lacked both copies of SMN l. There was no significant difference in the deletion frequency or subtypes among the 3 groups. Conclusions: Pulmonary cares are essential for SMA I with family histories in particular. Clinical manifestation of SMA Ⅱand SMA Ⅲ are of great heterogeneity for which a period of follow-up is necessary and differential diagnosis should pay more attention. There is no significant difference in the deletion frequency among the subtypes in electrophysiology and gene tests.