In dual-wavelength interferometry (DWI), by combing the advantage of the shorter synthetic-wavelength and the immune algorithm of phase ambiguity, we propose an improved phase retrieval method with both high accuracy and large measurement range, which is a pair of contradiction in the reported DWI method. First, we calculate the height of measured object at longer synthetic-wavelength through using the wrapped phases of two single-wavelengths. Second, by combining the immune algorithm of phase ambiguity and the height of measured object at longer synthetic-wavelength, we can perform the phase unwrapping of the larger one of the two single-wavelengths, then achieve accurate height at single-wavelength named as the transition height. Finally, we perform phase unwrapping of shorter synthetic-wavelength through using the immune algorithm of phase ambiguity and the transition height, and then the height at shorter synthetic-wavelength can be achieved. Compared with the reported method, in addition to maintaining the advantage of high accuracy, the proposed method does not need the additional wavelength, so the corresponding measurement procedures is greatly simplified. Simulation and experimental results demonstrate the performance of proposed method.