Diagnosis of mental retardation cannot be made by looking at the hands. Mental retardation is defined as a developmental period in which intellectual functioning is significantly lower than that of the same age, accompanied by adaptive deficits. According to the above definition, there are three diagnostic criteria for mental retardation as follows: intellectual functioning is significantly lower than the level of the same age, i.e., the IQ is lower than two standard deviations from the mean and below 70 points; there are concomitant deficits in adaptive skills such as social skills, verbal interactions, daily life care, and personal independence, to a degree that is much lower than that expected of a child of the same age in terms of literacy; and the onset of the disease occurs before the age of 18 years. The clinical manifestations of mental retardation are as follows: 1) slowing down of the speed of perception, it is easier to receive stimuli from the visual pathway than from the auditory stimulus; 2) severe distraction of attention, with a very narrow breadth of attention; 3) poor memory, after countless repetitions to be able to learn something, and then forgetting it all if it is not repeated; 4) poor verbal ability, only able to speak simple words; 5) low thinking ability, lack of ability to think in an abstract manner, imagination, and generalization; 5) low thinking ability, lack of the ability to think in abstraction In addition, they lack the ability of abstract thinking, imagination and generalization, not to mention the ability to learn by example; 6, basically no concept of numbers, relying on mechanical memory to learn simple addition and subtraction calculations; 7, emotionally unstable, poor self-control; 8, weak will, lack of self-confidence; 9, poor communication skills, it is difficult to learn to interact with each other. Parents and friends who find that their children have some of the above manifestations, please bring your child to the hospital in time for further diagnosis.