In this paper, we report on a distributed sensing system of phase-sensitive optical time-domain reflectometer (Φ-OTDR) based on bi-directional Raman amplification. With the bi-directional Raman amplification, the transmission loss of the optical fiber can be compensated efficiently. The experimental characterization of evenly detected signals along the whole sensing distance of 74 km with 20 m spatial resolution is successfully demonstrated, resulting in the longest distributed sensing system based phase-sensitive optical time-domain reflectometer reported so far, to the best of our knowledge. The influences of different incident powers and pump powers on Φ-OTDR are studied experimentally.