In order to recover the accurate phase distribution of the tested sample rapidly by the image plane digital holographic microscopy(IPDHM),the basic problems,such as accuracy,speed,applying scope and others of five kinds of phase unwrapping algorithms are studied by theoretical analysis and experimental verification.The results show that the lateral shearing interferometry method based on least square is the best and fastest way to recover the phase which has under-sampling problem.Branch cut method on quality-guided path following method may cause serious errors because of streaks phenomenon and some not unwrapped areas.The discrete cosine transform(DCT) method based on least squares and preconditioned conjugate gradient(PCG) method may result in great error because the error can be transferred in the under-sampling area.Therefore,the lateral shearing interferometry method based on least square is the optimal phase unwrapping algorithm in IPDHM.