Lateral shearing interferometry is a reference-free technique. The wavefront under test interferes with a laterally sheared copy of itself in the superposed range. The wave-front difference of the two sheared wavefronts is obtained from interferogram, the wavefront could be reconstructed using some wavefront reconstruction algorithm. The Zernike underdetermined coefficient method based on difference Zernike polynomial is one of the wavefront reconstruction algorithms. The measuring principle of lateral shearing interferometry is introduced; 2D shearing wavefront reconstruction based on decoupling difference Zernike under determined coefficient method is proposed. It is indicated by theoretical analysis and numerical simulation that the proposed method is simple, accurate and could be used to recover annular wavefront with Zernike polynomials in rectangular coordinates.