Developmental delay, also known medically as mental retardation, is a mental developmental disorder that manifests itself as a lower level of intelligence than children of the same age and is accompanied by deficits in adaptive behavior due to congenital or acquired factors that delay or hinder mental development. The disorders that cause developmental delay are different at different times, but the basic clinical features are mental retardation and social maladjustment, with delayed language comprehension and expression development being the most common. Children suspected of developmental delay must be detected early, diagnosed early, the causes identified, early intervention, graded intervention and integrated intervention, so that for some treatable diseases, a more satisfactory treatment effect can be achieved. For example, if the developmental delay caused by phenylketonuria is detected early and a low-phenylalanine diet is started, and iodine and thyroxine are given to children with cretinism early, then the child’s symptoms can be improved to the maximum and the child can grow up as normal with early treatment. If the child is already mentally retarded and mentally impaired for various reasons, the child can only be treated through active rehabilitation and educational interventions. Throughout the treatment process, follow up IQ tests to objectively assess the child’s condition. For some mental retardation due to genetic metabolic disorders, the prognosis is often determined by the timing of diagnosis and intervention, and early diagnosis and intervention can lead to a good prognosis. Appropriate family and educational interventions can help improve the child’s resilience and quality of life. Whether developmental delay can be cured depends on what causes it? Early diagnosis and intervention are important, as are educational training and the many factors inherent in the environment throughout the rehabilitation process.