The principle of localization of a small object in tissues using an amplitude cancellation phase modulation system (or phased-array system) is explained by an analytical model of the diffusion approximation. The effects of various factors on localization of the object using Phased-array system are discussed, which include the relative phase and the amplitude between two sources, the absorption coefficient and the size of absorbers. A localization method independent of the relative amplitudes and phase between two sources is presented. The principle of the method is explained and its feasibility is proved theoretically.