Inter-satellite communication needs near diffraction-limited laser. Wavefront testing of diffraction-limited laser is difficult through several techniques reported before. Double-shearing interferometer presented here including four wedges is designed on the basis of traditional Jamin lateral shearing interferometer. The wavefront aberration can be deduced from the different fringe spacing with half minimum wavefront height of single aperture. The apparatus and principle of the interferometer are explained. Some simulations and the experiment of 0.3 wavelength wavefront height are given also. Then it is clear that with this design it is easy to know the sign of the wavefront aberration and to evaluate the value by nakedeyes. The interferometer works in the equal optical path interference which is useful for laser diode etc. with shorter coherent length.