〔Abstract〕 Objective To investigate the application value of bone marrow cell morphology and serum free light chain (sFLC), lactate dehydrogenase (LDH) in the diagnosis of multiple myeloma (MM). Methods A total of 100 patients with MM diagnosed in Xinxiang Second People's Hospital from January 2019 to January 2022 were selected as the study subjects (observation group), and another 80 subjects who underwent bone marrow aspiration due to other reasons during the same period were selected as the control group. The proportion of bone marrow plasma cells and serum sFLC and LDH levels of the patients in the two groups were determined and analyzed, and the diagnostic value of the three indexes for MM was analyzed by receiver operating characteristic curve (ROC). Results The proportion of bone marrow plasma cells, serum levels of LDH, sFLC-κ and sFLC-λ in the observation group were higher than those in the control group, and the differences were statistically significant (P < 0.05). The proportion of bone marrow plasma cells and the levels of serum LDH, sFLC-κ and sFLC-λ in MM III stage were higher than those in MM II stage, MM I stage, the proportion of bone marrow plasma cells and the levels of serum LDH, sFLC-κ and sFLC-λ in MM II stage were higher than those in MM I stage, the differences were statistically significant (P < 0.05). Bone marrow cell morphology, serum sFLC and LDH had certain value in the diagnosis of MM, and the combined diagnosis had high sensitivity and specificity, which were 97.00 % and 72.00 %, respectively, and the area under the curve ( AUC ) was 0.916 (0.311-1.562). Conclusion The proportion of bone marrow plasma cells, and the levels of serum LDH, sFLC-κ and sFLC-λ in MM patients increased abnormally, and gradually increased with the severity of the patient 's condition, and the combined detection of MM had higher diagnostic efficiency.