Objective To investigate the clinical and electroencephalographic (EEG) features of CDKL5 gene-related early onset epileptic encephalopathy. Methods A total of 6 children diagnosed with early-onset epileptic encephalopathy from March 2013 to September 2021 and screened with CDKL5 gene variation by next-generation gene sequencing were collected. Their clinical data and EEG characteristics were analyzed retrospectively. Results The median onset age of six children was 2 months (45days-1 years), and the follow-up time was more than 1 year. All children initially had focal seizures that successively progressed to spasms, myoclonic seizures, tonic seizures, and atypical absence seizures over a period of days to 4.3 years. All the children had serious psychomotor and intellectual retardation or regression. The EEG of the children also evolved from the initial normal or focal or multifocal discharge into a highly irregular pattern, and the EEG showed a pseudo-periodic feature after 2 years of age. Among them, the EEG of one male child showed a highly irregular pattern in the early stage, and the dynamic evolution was not obvious in the course of the disease. All the CDKL5 gene variants in the 6 children were de novo variants, including insertion variants, missense variants and deletion variants. Several antiepileptic treatments failed to control seizures effectively. Adrenocorticotropic hormone (ACTH) and ketogenic diet were used in 3 patients, and growth and development were improved in 2 patients. Conclusions CDKL5-related early onset epileptic encephalopathy has early onset and mostly begins with focal seizures, and a variety of seizure types occur successively. The clinical and EEG abnormalities are more serious in boys, and the EEG of 5 girls shows a certain pattern of evolution. Different gene variation sites may have different early EEG manifestations. Epileptic seizures are not easy to control. The growth and development of some patients can be improved by administration of ACTH and ketogenic diet.