This paper reports on the fidelity of Stimulated Brillouin Scattering of single-cell with one focus (SCOF) and single-cell with two focuses (SCTF). The results showed that in the case of SCOF the fidelity of SBS decreased slightly with the pump energy increasing, but for the SCTF, the fidelity is sensitive to the length of the two focuses. When the length is short, the fedility is almost unchanged, however, when the length is long, the fidelity increased and the biggest enhencement is up to 13%. An explanation to this phenomenon is given. The experimental results support this interpretation.