Purpose: To investigate the correlation between multi-parameters of focal lesions and the ratio of bone marrow plasma cells (BMPC) by using whole body DWI and T1-mDIXON imaging in patients with multiple myeloma. Materials and Method:41 patients were collected with pathologically confirmed multiple myeloma from February 2015 to June 2018 including 21 males of aged 46-66 years (55.6+10.1 years) and 20 females of aged 42-66 years old (49.1±9.9 years). All patients underwent whole body DWI and T1-mDIXON examination before treatment based on a 3T MR scanner (Ingenia, Philips, Best, The Netherland). The ratio of bone marrow plasma cells (BMPC) was examined by bone marrow smear. The focal lesions of the Anterior superior iliac spine were detected and the corresponding ADC value, fat signal intensity (Mfat) and water signal intensity (Mwater) were extracted. The fat fraction (FF) was also calculated by dividing the signal intensity in the fat image by the corresponding in-phase mDIXON image. The Spearman correlation test was performed to evaluate the correlation between the above parameters of focal lesions with the ratio of BMPC. Result: There was high positive correlations between ADC value and BMPC ratio (r=0.776) as well as between the Mwater and BMPC ratio (r=0.985). And there was high negative correlations between Mfat and BMPC ratio (r=-0.985) as well as the FF and the BMPC ratio (r=-0.985). Discussion：DWI help to increase the lesion detection through qualitative assessment and can furtherly increase the diagnostic confidence of focal lesions by using ADC measurements. After multiple myeloma cells invading the bone marrow, the normal structure of the bone marrow is destroyed and osteolytic changes are formed. The increase in the number of tumor cells leads to an increase in normal bone marrow destruction, which leads to a decrease in extracellular space and a severe osteolytic change, which could be represented by ADC values. Due the increasing of water content and the destruction of normal fat cells in the bone marrow, Mfat and FF decreased as the bone marrow invasion developed. Conclusion：There is a high correlation between Mfat, Mwater, FF value, ADC value and the ratio of bone marrow plasma cells, which is beneficial for assessing the degree of bone marrow invasion.