Objective To analyze the correlation between the thickness of the rectus abdominis muscle and the staging of malignant tumors in patients with malignant tumors. Methods: 65 patients of malignant tumor patients who were treated in our hospital from June 2022 to June 2023 were selected. Patients in the malignant tumor group were divided into no cachexia group( 11 patients ), pre-cachexia group( 15 patients ), cachexia group( 28 patients ), and cachexia refractory group( 11 patients ) using the cachexia score table, and 42 patients were selected as the healthy group.The rectus abdominis thickness and abdominal median subcutaneous fat thickness were measured. The differences of rectus abdominis thickness, abdominal median subcutaneous fat thickness and the ratio of rectus abdominis thickness to BMI between the malignant tumor group and the healthy group were compared, and the differences of these indexes between the malignant tumor groups were compared. The correlation between rectus abdominis muscle thickness and cachexia stage was analyzed.