The single crystal yield surfaces (SCYS) of b.c.c. crystals for {110}<111>, {112}<111> and {123}<111> multiple slip have been analyzed systematically on the basis of Taylor/Bishop-Hill crystal plasticity theory. The complete yield vertices of single crystal have been derived when their critical resolved shear stresses (CRSS) are equal. The correspondingly active slip systems and the number of sets of five independent active slip systems have been obtained. Furthermore, all these possible yield stress states have been classified and tabulated according to the crystal symmetry.