The present invention provides a detection reagent and therapeutic target for B cell tumor after targeted therapy and related applications. The reagent composition comprises 3 groups of antibodies, with the first group of antibodies including an anti-CD38 antibody, an anti-CD10 antibody, an anti-CD34 antibody, an anti-CD19 antibody, an anti-CD24 an antibody, an anti-CD20 antibody, an anti-CD81 antibody, an anti-CD45 antibody; the second group of antibodies including an anti-CD38 antibody, an anti-CD10 antibody, an anti-CD34 antibody, an anti-CD19 antibody, an anti-CD20 antibody, an anti-CD72 antibody, an anti-CD45 antibody; and the third group of antibodies including an anti-cytoplasmic CD79a antibody. The reagent composition of the present invention can be applied for the detection of B-lymphocyte tumors after targeted therapy by flow cytometry.