The reconstructed optical field phase of speckle interference fringes generally has high spatial variation frequency.However,the space-band width is so limited that it is easy to int roduce undersampling and to cause the existence of massive unreliable data points in the wrapped phase,which increas es the difficulty of phase unwrapping algorithm.This paper introduces the principle of shearing interferometry into f our directions least-square phase unwrapping algorithm by reconstructing two-dimensional optical field for the wr apped phase,in order to reduce the influence of discontinuity of phase discrete gradient and the impact of undersam pling.On one hand,the disadvantage of the phase truncation can be eliminated.On the other hand,the ability of proc essing the wrapped phase can be improved.Related experiments are carried out to verify the algorithm.The result s indicate that this algorithm could suppress the error transfer effectively.It is suitable for phase unwrapping of s erious wrapped regions and it has better results than the original algorithm.