Five probands with spastic paraplegia and ataxiaphenotype in the outpatient department were selected as subjects. High-throughput sequencing chips combined with capillary electrophoresis were used to detect the dynamic mutations of pathogenic genes in the probands. One proband was found to carry 84 CAG repeats in the ATXN3/MJD1 gene， and his sister and father carried 82 and 73 CAG repeats， respectively； thus， this family was suspected to have a hereditary spinocerebellar ataxia type 3/Machado-Joseph disease （SCA3/MJD） pedigree， and had obvious clinical heterogeneity and anticipation. It is suggested that patients with spastic paraplegia and cerebellar ataxia phenotype， especially those with a family history of dominant inheritance， shall undergo adynamic mutation detection of SCA3 pathogenic genes； at the same time， members with normal phenotype in their families should undergo a careful physical examination to avoid missed diagnosis.