The location of fiber Bragg grating (FBG) is one of the key technologies for the fabrication and the laying quality of the large ultra-weak FBG array. Aiming at solving the problems existing in the traditional optical time domain reflector for locating ultra-weak FBGs, a two-dimension location method based on phase and intensity is proposed. The method interrogates the single FBG with optical time domain techniques, and locates the target FBG by adjusting the phase difference between the input pulses and the selection pulses and detecting the peak power of reflective signal. The system for the FBG array is constructed to locate the 1009-FBG array with the average reflectivity of -34 dB and the spatial space of 2.5 m, and the 0.1 m position error is obtained.