A color CCD camera are adopted to make sure shearography can be applied in large deformation of objects dual-wavelength lasers illumination. By separating the spectrum in the Fourier domain, the subtraction of the red wavelength phase and the green wavelength phase yielded a new phase distribution of a synthetic wavelength. After filtering in frequency domain and phase unwrapping, the continuous phase can be gotten. The number of phase stripes of synthetic wavelength is 0.189 times smaller than that of single wavelength by theoretical derivation. Using the synthetic wavelength can reduce the phase fringe density effectively, and solve the sub-Nyquist sampling problem, which are caused by too intensive interference fringes in object′s deformation. In addition, it also reduces the difficulty of image processing in filtering and phase unwrapping, enhances the reliability of image processing, and improves the measurement accuracy. Phase comparing between synthetic wavelength and single wavelength were given. Moreover, the fringe densities of the two kinds of wavelengths at the same external force also were compared. Experiments verify the effective, accuracy, and reliable of this method. It can process the large deformation measurement of composite material and dramatically expand the measurement rang of shearography in engineering application. It also provides a reference for the designing new type system of shearography.