根据谱整形的思想将脉冲预抽运的概念引入布里渊光时域反射系统，提出了一种提高传感性能的方法。该方法利用由预抽运脉冲和传感脉冲组成的阶梯脉冲作调制信号，通过预抽运脉冲和传感脉冲的受激布里渊作用实现布里渊谱的整形和传感信号的放大，可有效地解决系统空间分辨率和测量精度的矛盾，并可提高系统信噪比，增加传感距离。通过受激布里渊稳态方程的瞬态分析对阶梯脉冲调制布里渊光时域反射系统中的受激布里渊散射模型进行了求解，对阶梯脉冲进行了最佳化设计，比较了矩形脉冲、洛伦兹形脉冲和阶梯脉冲调制时的系统性能。结果表明，当预抽运脉冲和传感脉冲参数为50 ns、0.2 W 和2 ns、1 W 时，采用阶梯脉冲时的布里渊谱宽约为44 MHz，10 km 光纤末端信噪比较采用矩形脉冲时提高了7.97 dB。最后，通过实验验证了所提方法的可行性。

A new method to improve the performance of Brillouin optical time domain reflectometer (BOTDR) system is proposed, by introducing the reported pulsed pre-pump technique into the well known structure based on the consideration of Brillouin spectrum reshaping. In this method, the optical pulse launched into the fiber is provided by electro-optical modulation with a step pulse composed of a pre-pump pulse and a sensing pulse. The reshaping of Brillouin spectrum and the amplification of sensing signal are achieved through the stimulated Brillouin scattering (SBS) interaction between pre-pump pulse and sensing pulse, and the contradiction between spatial resolution and measurement accuracy can be solved, effectively. Meanwhile, the signal to noise ratio and the sensing distance can be enhanced significantly. SBS models under steady-state are solved by transient analysis in the step pulse modulation BOTDR, the optimal design of step pulse is made, and the system performance is compared with those in rectangular pulse and Lorentz pulse modulation structures. The results show that with a step pulse synthesized by a pre-pump pulse with a width of 50 ns and a peak power of 0.2 W and a sensing pulse with the corresponding parameters of 2 ns and 1 W, Brillouin spectrum width can be as narrow as about 44 MHz, and the signal to noise ratio at the end of 10 km single mode fiber can be 7.97 dB higher than that in the rectangular pulse structure. Finally, the feasibility of the proposed method is demonstrated experimentally.