To investigate the negative effects of the relative intensity noise (RIN) of the Raman pump and the Brillouin slow light on the long-distance Brillouin optical time-domain analyzer (BOTDA) assisted by distributed Raman amplification (DRA), the coupled amplitude equations describing the interactions between the Raman pump, Brillouin pump and Brillouin probe have been solved. Results of RIN transmission of the Raman pump show that 1 dB increase in the RIN of the Raman pump leads to about 1 dB decrement in the signal-to-noise ratio (SNR) of the received electrical signal. This undesirable effect can be ignored when the RIN value of the Raman pump is down to -135 dB. Furthermore, results of Brillouin slow light show that compensating the linear loss of the waves in the sensing fiber by DRA results in an increase of position locating error (PLR) induced by Brillouin slow light effect. It′s also shown that, at the same time, point in the detected signal traces obtained at different sweeping frequencies corresponds to different spatial locations on account of PLR. The errors will have a significant negative effect on the reconstruction of the 3D Brillouin spectrum and the accurate extracting of the Brillouin frequency shift of the sensing fiber.