In darkpulse Brillouin optical time domain analyzer (DPBOTDA) DPBOTDA the effective sensing length is greatly limited by the severe interaction between the QuasiCW pump light and pump light. A simple DPBOTDA was proposed to prolong the total sensing length without using multisection fibers. To mitigate the impact of the high power QuasiCW pump light, both Brillouin gain and loss effect along fiber were measured simultaneously in this scheme, yielding the Brillouin signal by subtracting the two side bands of the optical carrier suppressed (OCS) Stokes light. Based on this proposal, the total sensing length in DPBOTDA could be increased. Simulations and discussions were conducted to validate the proposal, and the results are useful for designing high spatial resolution distributed Brillouin fiber sensor.