Objective: To analyze the ultrasonographic features of low-grade myofibroblastic sarcoma (LGMS) and explore its preoperative diagnostic value and key points of differential diagnosis. Methods: A case of LGMS confirmed by surgical pathology was retrospectively analyzed. The ultrasonographic manifestations were combined with magnetic resonance imaging (MRI) and pathological results for comprehensive analysis, and relevant literature was reviewed. Results: The patient was a 41-year-old female with a hypoechoic mass (45 mm × 30 mm × 21 mm) in the muscle layer of the left lower leg. The mass had an irregular shape with lobulated margins, and some boundaries were unclear. A large hyperechoic area (8.0 mm × 1.6 mm) was seen inside. Color Doppler flow imaging (CDFI) showed rich blood supply around and within the mass, and a cord-like extension was visible at the lower edge. MRI showed an isointense signal on T1-weighted images and a long T2 signal, with high signal intensity on diffusion-weighted imaging (DWI) and significant enhancement on contrast-enhanced scans. Postoperative pathology confirmed LGMS. Conclusion: The ultrasonographic manifestations of LGMS have certain characteristics, but a definite diagnosis still depends on pathological examination. Ultrasonography can provide important imaging evidence for preoperative assessment.