Undernutrition is a lack of essential nutrients in the body of children, seriously affecting the development and growth of young children. Undernourished children often have poor immunity, are susceptible to diseases and have a slower recovery than other normal children. Our study was conducted using a case-control method on 270 children with pneumonia, including a patient group of 90 malnourished children and a control group of 180 non-malnourished children, with the aim of describing the clinical and paraclinical characteristics and treatment outcomes of pneumonia in malnourished children. The results showed that undernourished children had more severe clinical and paraclinical symptoms and a longer treatment time for symptoms used more antibiotics in combination and had to change antibiotics more often than nonundernourished children (p<0.05). The study's conclusion shows that more attention should be paid to the health of undernourished children. When children are sick, special care is needed to help them recover and get well.