Triangle interferometer is the simplest ring-type interferometer. Its advantages include roughly equal optical path, high measuring accuracy and continuous shearing amount. However, its nature of shearing interference brings about complexity in quantitative investigations. If a Ronchi grating is placed in front of the triangle interferometer, optical beam is diffracted. The zero-order andiffracted beam and first-order diffracted beam are taken as the object beam and reference beam, respectively. They are combined to form interference fringes in the triangle interferometer. In this way, characteristics as a triangle interferometer remain, while lu terference between same points on the wavefront is realized, thus making data processing much easier, Sinee the two beams are very near to each other, they are able to transmit fchroagii the same optical component so that the optical system becomes simple and easily adjustable, A grating-triangle interferometer is fully competent in obtaining interferograms of laser plasmas which require a time resolution up to lops. Homogeneity of refractive index and thickness of ordinary transparent media can also be measured with a grating-triangle interferometer. Interferograms of laser plasmas and Nd-glass laser rods have been obtained by using ihis interferometer.