Abstract: A new technique of real time visualizing and quantitatively measuring of rocket exhausted plume field is presented in this paper.The beam source is a He-Ne laser and a alignment optical system to provide a parallel light beam 300mm in diameter. Then the parallel light beam goes through the plume field and two 20line/mm Ronchi gratings to obtain a diffraction pattern,and the pattern imaged at a CCD sensor to display on a monitor and been recorded.By means of image computer processing and Gladstone-Dale formula,with the parameters of grating index P,shift of more fringe,interval of more fringe,and interval of two gratings,the density distribution of the plume field can calculated.