Chimeric antigen receptor (CAR)-modified T cell therapy is increasingly administered for hematological malignancies. Cytokine release syndrome (CRS) is a common and severe complication of CAR-T therapy. In the present case, a 62-year-old male patient was diagnosed with relapsed and refractory multiple myeloma (RRMM). Treated with CART-CD19/BCMA therapy, his symptoms remitted, during which occasional but severe CRS associated with coagulation disorder still appeared, as evidenced by the coexistence of a huge thrombosis and bleeding tendency. Through the First Generation Sequencing, we extracted genomic DNA from the patient's peripheral blood to analyze the distribution of polymorphism at the -572C/G site of the promoter of IL-6 gene. The results showed that the genotype of -572C/G promoter polymorphism was CC, indicating that high level of IL-6 and -572C/G polymorphism might be associated with the risk of thrombotic disorders. We concluded that immediate diagnosis and appropriate treatment of coagulopathy could reduce CRS-related mortality.