Abstract: As an important direction finding technique, phase interferometer is widely used in radar and electronic warfare area. In order to solve the phase ambiguity problem of the interferometers, study based on the phase sample space theory is carried out in the paper. In terms of dual-baseline interferometers, the physical nature and intrinsic mechanism of phase ambiguity resolution is analyzed and revealed, and a general theoretical model on the correct ambiguity resolution for interferometers is established; furthermore, the correct probability formula for the ambiguity resolution of multi-baseline interferometers is derived. On this basis, a baseline optimization and efficient ambiguity resolution algorithm for interferometers is proposed in this paper. It improves the ambiguity resolution performance of the interferometers remarkably by choosing the optimum combination of baselines in different working frequency bands and making full use of the theoretical intervals of correct ambiguity resolution, while relaxing the array constraints. Theoretical analysis and simulation experiments show that the proposed algorithm not only reduces the constraints on the array configuration and broadens the scope of application of the algorithm, but also has a lower computational complexity, offering an excellent prospect for engineering application.