The clinical manifestations of mental retardation are mainly the following: slowed perception, easier to receive visual pathway stimuli than auditory stimuli, severely distracted attention, very narrow attention span, poorer memory, it takes numerous repetitions to learn some knowledge. If not learned through repetition, it is forgotten quickly, poor verbal ability, can only speak very simple words, relatively low thinking ability, lack of abstract thinking ability, imagination and generalization. Basically, they have no concept of numbers and can learn simple addition and subtraction calculations by mechanical memory. Emotionally, they can be characterized by emotional instability, poor self-control, weak will, lack of self-confidence, poor interpersonal skills, and difficulty learning interpersonal interactions. In terms of examination, routine tests such as blood and urine, cerebral fluid, biochemistry, etc., intelligence tests and behavioral assessment can help diagnose mental retardation.