Objective: This study aims to investigate the predictive role of baseline body composition parameters，including specifically myosteatosis, sarcopenia, and the cachexia index, on disease-free survival (DFS) in patients with gastrointestinal stromal tumors (GIST) receiving postoperative imatinib therapy. Methods: This single-center retrospective study included 82 moderate- or high-risk GIST patients who underwent tumor resection and were pathologically diagnosed at the First Affiliated Hospital of Nanjing Medical University between January 2014 and December 2018. Body composition parameters including skeletal muscle index, subcutaneous and visceral adipose index, and low-attenuation muscle area were quantified via CT imaging at the L3 vertebral level to assess the presence of myosteatosis or sarcopenia in patients. Univariate and multivariate Cox proportional hazards regression models were employed to analyze the relationship between these parameters and DFS. Kaplan-Meier survival curves were generated, and the model's predictive performance was evaluated using receiver operating characteristic (ROC) curves, calibration curves, and decision curve analysis (DCA). Results: The median follow-up duration for the 82 patients was 72 months, with 22 cases (26.83%) experiencing recurrence during this period. Multivariate Cox regression analysis revealed that myosteatosis (P=0.010), high-risk status (P=0.011), and C-KIT exon 13 mutation (P=0.002) were independent risk factors for DFS. The nomogram based on these factors yielded area under the ROC curve of 0.728 and 0.746 for DFS at 3 and 5 years, respectively, indicating strong predictive performance. Additionally, decision curve analysis confirmed the nomogram’s utility in clinical decision-making. Conclusion: Myosteatosis, risk stratification, and C-KIT exon mutation types represent important prognostic factors for DFS in GIST patients. Compared to sarcopenia, myosteatosis shows greater clinical value in predicting prognosis and may serve as a novel prognostic factor for GIST patients.