Objective This study aimed to investigate the nutritional status of children newly diagnosed with malignant solid tumor and the changes during therapy, and to identify factors associated with malnutrition during therapy. Method We enrolled 104 children with malignant solid tumor received inpatient treatment at the Department of Hematology and Oncology in Nanjing Medical University Affiliated Children’s Hospital between March 2018 and September 2019 . STRONGkids was used for nutritional risk screening. Dietary intake was analyzed within 24 h, and nutritional status were assessed according to WHO 2006 child growth standards. The influencing factors of malnutrition after 3 months of treatment were analyzed. Results At diagnosis, there were 61 males and 43 females, with a median age of 4 . 5 years old, 27 . 9 % of the patients were malnourished, BMI-Z decreased significantly after treatment, and the difference was statistically significant (P< 0 . 05 ). During anticancer therapy, the incidence of malnutrition rose to 48 % after 3 months. Logistic regression showed that the nutritional status at diagnosis and STRONGkids nutritional risk score were positively associated with a higher proportion of malnutrition (P< 0 . 05 ). Conclusion Children with solid tumor are prone to nutritional deterioration during treatment. For children with malnutrition and high nutritional risk score, reasonable nutritional support intervention should be given as soon as possible.