Acute myeloid leukemia (AML) combined with small B-cell lymphoma in the bone marrow is very rare. This article reported a case of typical AML with synchronous small B-cell lymphoma in the bone marrow. At the early onset, the bone marrow blasts, peripheral blood blasts and the abnormal lymphocytes accounted for 86%, 50%, and 25%, respectively. AML was taken into consideration based on pathology and immunohistochemistry result of bone marrow biopsy. Cytogenetic examination reported 45, XY, –21[4]/45, XY, –3, +12, –21[2]/46, XY[14]. The patient was treated with idarubicin combined with cytarabine (IA regimen) chemotherapy. After 2 weeks, bone marrow blasts decreased to 28%, while abnormal lymphocytes increased to 64%. The patient was treated with IA regimen again in addition with dexamethasone (10 mg/d). Two weeks later, no blasts were found in the bone marrow, but the abnormal lymphocytes still accounted for 79%. The patient was treated with R-CHOP chemotherapy. Half a year later, the bone marrow blasts accounted for 97%. He was given piraubicin combined with cytarabine (TA regimen) chemotherapy for 3 months before his death. During the whole process of treatment, the ebb and flow of bone marrow blasts and abnormal lymphocytes indicated poor response to myeloid and lymphatic treatments and short survival. Combined with the clinical data, treatment outcome and literature review, we can further improve the understanding of AML with synchronous small B-cell lymphoma in the bone marrow.