Objective To investigate the value of blood index and 18F-FDG PET/CT in lymph node metastasis of malignant melanoma. Methods The blood indexes of 17 patients with malignant melanoma admitted to our hospital from July 2020 to May 2023 were collected. The di?erences of 6 blood indexes between lymph node metastasis group and non-metastasis group and the results of PET/CT examination were analyzed. Pearson correlation was used to analyze the correlation between SUVmax value and di?erential blood indexes. Results The level of LDH in the metastasis group was higher than that in the non-metastasis group (P<0.05), while there was no signifcant di?erence in albumin, globulin, CRP, NLR and PLR between the two groups (P>0.05). There was a positive correlation between LDH and SUVmax in lymph node metastasis group (r=0.417, P<0.05). Conclusion LDH and 18F-FDG PET/CT have a certain value in the diagnosis of lymph node metastasis of malignant melanoma.