Dual-wavelength digital holographic microscopy technique has many important applications in the imaging of biological cells. It has some significant advantages, such as the large measurement range and no phase unwrapping procedures. However, the multi-steps image is required in synchronous interference microscopy, it is not suitable to perform real-time dynamic imaging of samples. In this paper, in order to meet the research and clinical application of dynamic imaging of living cells, a phase recovery algorithm is proposed in dual-wavelength interference and one-step microscopic imaging. This algorithm is on the basis of the principle of the digital holographic off-axis synchronous microscopy image. In this algorithm, only by means of Fourier transform, filtering, frequency-shifting operations, inverse Fourier transform to the dual-wavelength off-axis microscopic interferogram, the continuous phase of the sample can be calculated. Simulation result of the lymphocyte shows that this method is feasible, and the error analysis suggests that it has good accuracy. This approach is free of phase unwrapping, and has no the calculation of the phase shift and no the multi-step imaging. It can recover the phase distribution only from one dual-wavelength interferogram. So it has a high potential application for the technology development, and can be applied to accurate dynamic imaging of biological cells and tissues.