The normal performance of four-month-old infants is mainly in the areas of physical development, motor function, emotional expression and perceptual development. 1. Physical development: There are obvious changes in the physical development of 4-month-old infants, and it is necessary to refer to the weight-height graph, as the height and weight of different infants may vary. 2. Motor function: 4-month-old infants’ motor function begins to develop slowly, and they can roll over and perform simple head lifting and head shaking, and their hands can grasp things or appear to be dancing. 3. Emotional expression: four-month-olds begin to show a lot of emotions, can communicate with others with simple emotions, will be teased by others, appear to smile or make a huh sound, the number of cries will also be reduced. 4. Perceptual development: four-month-old infants central nervous system development is relatively fast, visual, auditory, olfactory, tactile and other perceptions also have different degrees of development, can feel the external sound, color, smell, etc., can feel the stimulation of external objects, and then make different degrees of response. However, due to the different physical qualities of four-month-old infants, the developmental performance is also different, there will be some differences, daily parents should pay more attention to observation, timely detection of the infant’s behavior and a variety of needs, if any abnormalities, timely access to medical care.