The concept of pulsed pre-pump was introduced into Rayleigh Brillouin optical time domain analysis system. A step pulse composed of a sensing pulse and a pre-pump pulse modulated by microwave was used as the modulation signal in the system. The reshaping of Brillouin scattering signal in time domain was achieved through the stimulated Brillouin scattering interaction between Rayleigh scattering generated by the first-order sidebands of time-limited microwave-modulated pre-pump pulse used as the probe wave and the sensing pulse, by which the nonlocal effect was also reduced. The reshaping of Brillouin scattering signal in spectrum domain was achieved through the stimulated Brillouin scattering interaction between the zero-order baseband of microwave modulated pre-pump pulse and the sensing pulse, by which the contradiction between spatial resolution and measurement accuracy was effectively resolved. The transient coupled wave equations were calculated by applying frequency domain analysis method, through which the analytical model of stimulated Brillouin interaction occurred in the fiber during the propagation of the step pulse light was set up. When the sensing pulse is with a width of 5 ns and a power of 100 mW, and the pre-pump pulse is with a width of 50 ns and a power of 16 mW, the simulation results show that, in the fiber length of spatial resolution of 0.5 m, stimulated Brillouin scattering gain with fiber position takes the maximum value at 0.14 m, then decreases linearly to the fiber position of 0.37 m, but in the rest of fiber positions it is approximately zero. The Brillouin spectrum width in pre-pump pulse Rayleigh Brillouin optical time domain analysis system is about 35 MHz, which is only about 1/6 times of 212 MHz that is in the traditional Rayleigh Brillouin optical time domain analysis system, so the measurement accuracy can be improved under the same spatial resolution.