Phase-sensitive optical time domain reflectometer (Φ- OTDR) has great potential in many security applications,such as safety monitoring of pipelines,airports,borderlines and other long-distance perimete rs.The detection range,resolution, and signal-to-noise ratio(SNR) are tightly related parameters and influence each other,so all of the m should be considered together to achieve effective and reliable measurements.By combining the coherent detection and the forward Raman amplification,a novel Φ-OTDR system is proposed and de monstrated in this paper,which offers long distance sensing ability with high spatial resolution and high SNR.By optimizing the Raman peak power and its input power,the nonlinear effects of the system performance are d ecreased significantly. Furthermore,the coherent detection method can further improve the SNRs of the s ensing signal.Experimental results show that the proposed Φ-OTDR system′s high performance can be achieved with a long sensing distance of up to 103km with a spatial resoluti on of 15.7m,and an SNR of 7.89dB,which is the longest distance reported as far as we know.And the system is verified in a field pipeline trial on multi-point intrusion detection ability.