Brillouin optical time-domain reflectometer (BOTDR) can perform distributed strain measurement along an optical fiber. Its highest spatial resolution is limited to 1 m because of the restricted probe pulse width. Because the time to accomplish one single sampling by BOTDR cannot be neglected compared to probe optical pulse width, a novel multi-Lorentz fitting method based on equivalent optical pulse (EOP) is proposed to improve its spatial resolution. In this method, the equivalent optical pulse is obtained by integrating the probe optical pulse over the time to accomplish one single sampling by BOTDR and the backscattered Brillouin signal (BBS) received by BOTDR is decomposed into sub-BBSs according to the shape of equivalent optical pulse. Then the backscattered Brillouin signal is fitted by multi-Lorentz function to obtain central frequency of each sub-BBS. The strain in the length corresponding to each sub-backscattered Brillouin signal can be obtained by use of the dependence of Brillouin frequency shift on strain. It is experimentally demonstrated that the spatial resolution for strain measurement with BOTDR is improved to 0.05m by the proposed method.