Malnutrition is a problem affecting tumor patients greatly. This study aims to investigate whether demographic characteristics are related to the malnutrition of cancer patients. Twenty-three thousand nine hundred and four (23,904) patients with 16 common malignant tumors were enrolled in the study. Patient Generated Subjective Global Assessment (PG-SGA) was used as a screening tool to assess the nutritional risk of patients and analysis of variance was used to compare PG-SGA scores of patients. Correlations between PG-SGA scores and demographic characteristics were evaluated by correlation analysis. We observed that 57.88% tumor patients had some degree of malnutrition (score ≥4) and only 20.61% were well-nourished (score 0-1). Screening scores were higher among older patients for most of the tumors. PG-SGA scores showed the significant difference between females and males in some tumors. In addition, the PG-SGA scores of some tumors were significantly different in various types of medical insurances, education levels, occupations, regions, and nationalities. Correlation analysis indicated the existence of associations between PG-SGA scores and demographic characteristics. Understanding the distribution of nutritional risk of tumor patients and the correlations between the PG-SGA scores and demographic characteristics could help identify subgroups who may benefit from targeted interventions to improve the effect of clinical treatment and the quality of life for oncology patients.