This paper presents the operating principle of a new lateral shearing interferometer. It uses a Twyman-Green interferometer as a splliter, a grating obtained from interference fringes with a tested phase object as a detective element to elimilate system errors. The merits of this interferometer are adjustable sensitivity, antivibration and very large aperture. We used the interferometer with large-aperture to detect flow fields intsuper-sonic wind tunnels and rocket exhaust plumes and obtained important results.