Hematological tumor is the most common type of tumor in pediatrics. Children with hematological tumor are always accompanied by malnutrition due to metabolic stress and accelerating growth. At the same time, various anti⁃tumor treatments may also exacerbate malnutrition. Malnutrition includes undernutrition which result in energy and nutrient deficiencies, and overnutrition due to excess energy intake. Severe malnutrition could influence therapeutic effect, raise the risk of complications, prolong hospital stays, decrease quality of life, and even increase the risk of death. Nutritional screening at the initial stage of disease diagnosis, comprehensive and accurate assessment of nutritional status, and individualized nutritional support are of great significance for improving the prognosis of children with hematological tumors. In this review, the recent progress on the selection of nutritional screening tools, the content of nutrition assessment, the association between malnutrition and the clinical outcomes in children with hematological tumor were discussed. This article was written with a view to increasing the concerns of medical staffs about the nutritional status in children with hematological tumors, providing clinical basis for the reasonable selection of nutritional screening tools and nutritional assessment content, and improving the quality of life and clinical outcome of malnourished children through early nutritional interventions.