We report the influence of optical simple pulse coding on the Brillouin optical time domain analyzer (BOTDA) based on bi-directional Raman amplification. This method is proposed to reduce the frequency uncertainty in long-distance BOTDA under higher spatial resolution. The experimental characterization of 49.6 km temperature sensing with a measurement accuracy of ~1 ℃ under ~2.5 m spatial resolution over the whole length of sensing fiber is demonstrated. The signal-to-noise ratio (SNR) and the optical signal power distribution characteristics of the system are studied experimentally in this paper.