Aiming at the problem that the phase sensitive Φ-optical time domain reflectometer(Φ-OTDR) system can't locate the two adjacent sources whose spacing is less than its pulse width, this paper analyzes the high-order harmonic characteristics ofΦ-OTDR signal and its spatial distribution characteristics under the condition of two adjacent sources, and proposes a location method based on the bispectrum marginal spectrum. This method can improve the locating ability of Φ-OTDR without any additional hardware. The experiments show that this method can separately locate two vibration sources with 5 m interval under 200 ns probe pulse (means 20 m spatial resolution) and it can work no matter the same or different frequencies the two vibration sources are. This work will help the application of Φ-OTDR system in pipeline safety monitoring and structural health monitoring.