Objective To investigate the nutritional status and body composition of hospitalized cancer patients analyze the differences and correlations in nutritional status of inpatients in oncology department of different genders and different ages and provide an evidence for the implementation of nutritional therapy for cancer patients. Method Retrospectively analyze the nutritional status and body composition of 411 inpatients who were in the oncology department Cancer Center Changzhou Second People's Hospital Affiliated to Nanjing Medical University from July 2020 to April 2021 who applied the clinical nutrition analyzer for nutritional diagnosis and treatment. The patients were divided into non - elderly group < 65 years old and elderly group ≥ 65 years old . The body composition nutritional status of cancer patients of different genders and different ages and the correlation between phase angle and nutritional risk screening and nutritional assessment were analyzed. Result The incidence of nutritional risk was 44. 77% NRS 2002≥ 3 points the incidence of moderate malnutrition and severe malnutrition were 37. 23% PG-SGA was 4 - 8 points and 37. 47% PG-SGA≥9 points respectively among all patients. Among male patients compared to non-elderly group the body weight muscle mass total water content and skeletal muscle indexes of the elderly group were significantly decreased which was statistically significant 64. 88± 10. 26 kg vs 59. 42 ± 10. 75 kg 49. 1 ± 6. 86 kg vs 44. 95 ± 5. 93 kg 38. 32 ± 5. 27 kg vs 35. 15 ± 4. 58 kg 28. 64±4. 56 kg vs 25. 84± 3. 91 kg P< 0. 05 the incidence of nutritional risk and severe malnutrition increased significantly 24. 18% vs 56. 25% 20. 88% vs 46. 53% P<0. 05 . Among female patients compared to non-elderly group there was no significant difference in body composition indexes of elderly patients P > 0. 05 but the incidence of severe malnutrition increased significantly 32. 39% vs 42. 86% P<0. 05 . Phase angle was negative correlated with nutritional risk and malnutrition in cancer patients of different sexes and ages significantly. Conclusion The incidence of severe malnutrition in elderly cancer patients in oncology department has increased significantly and the body composition indicators of male patients have decreased significantly. Clinically body composition and nutritional status of elderly male cancer patients should be given more attention.