The invention provides a fused protein with extracellular fragments of a macrophage stimulating factor receptor (cFms). The fused protein is formed by connecting the cFms extracellular fragments and human immunoglobulin Fc by a connecting peptide and is named as cFmsECD-Fc. The cFms extracellular fragments are composed of at least two of five immunoglobulin (IgG) extracellular structure domains. The formed fused protein comprises YY-001, YY-002, YY-003, YY-004, YY-005, YY-006 and YY-007. The fused protein provided by the invention has functions of combining interleukin-34 (IL-34), combining the macrophage stimulating factor receptor (M-CSF) and blocking the combination of IL-34 / M-CSF ligand and common receptor cFms, and is suitable for treating diseases caused by the IL-34 / M-CSF under an abnormal condition. The fused protein is promising in the treatment on autoimmune diseases, inflammatory diseases, osteoporosis and tumor. And the fused protein is used for preparing medicines capable of inhibiting the inflammatory diseases, medicines capable of inhibiting the osteoporosis caused by osteoclast or medicines capable of inhibiting the growth and metastasis of the tumor.