Objective To investigate the clinical features of myotonic dystrophy （DM）， and to evaluate the value of electromyography （EMG） and target gene detection in the diagnosis of DM.Methods A retrospective analysis was performed for the clinical features， EMG findings， and target gene detection results of six patients with DM from four different families.Results All six patients were found to have the clinical manifestations of various degrees of myotonia， muscle weakness， amyotrophy， and multi-system involvement. EMG showed a positive rate of 100% for myogenic damage with myotonic discharge， and Nerve Conduction Study showed a reduction in the amplitude of compound muscle action potential in some motor nerves in three patients， with normal results in the other patients. Target gene detection showed an abnormal amplification rate of 100% for CTG repeat in the 3′ untranslated region of the dystrophia myotonica protein kinase gene， with a number of >50， while normal CCTG repeats were observed in the first intron of the zinc finger protein 9 gene.Conclusions In the diagnosis of DM， positive family history and typical clinical features are the basis for diagnosis， and EMG is a preferred method for diagnosis and screening， with a higher positive rate in DM type 1. Target gene analysis is the gold standard for diagnosis and typing.