Abstract: Objective: To explore the application value of spectral CT multi-material decomposition (MMD) algorithm in the grading of secondary lower extremity Lymphedema. Materials and methods: Prospective collection of patients who underwent spectral CT admitted to our hospital from June 2019 to June 2020 were prospectively collected. The spectral CT images were analyzed by two radiologists with more than five years of experience in CT diagnosis. The volume of the both lower limbs were measured using the threshold value software. Based on the percentage increase in the volume of the affected side compared to the healthy side, the enrolled patients were divided into three grades: mild, moderate, and severe. Percentage fat volume fraction (FVF) images were generated by using the MMD algorithm on spectral CT to measure the fat content of the affected and healthy lower limbs respectively. Paired <i<t</i< test were used to analyze the difference of the percentage FVF between the affected and healthy side in mild, moderate, severe patients. Results: Forty patients (female/male, 36/4 cases, with age range of 32-71 years old, median age of (53±10) years) were finally enrolled, and the course of disease was (3±5) years. There were 8 cases in mild group, 14 cases in moderate group and 18 cases in severe group. There were statistical differences in the percentage FVF between the affected and healthy side in mild, moderate and severe patients. There was no statistical difference in the percentage FVF of the affected side among mild, moderate and severe patients.Conclusion: The spectral CT MMD algorithm can quantify the percentage FVF of Secondary Lower Extremity Lymphedema, but it cannot be used alone in the grading of secondary lower extremity lymphedema.