Digital Speckle Pattern Interferometry (DSPI) is one of modern optical measurement techniques. It has the advantage of non-contacting, whole field, high measurement accuracy and without special process of the surface to be measured. With the development of computer science and electronics, DSPI is used more and more widely. This paper systematically presents the principle of speckles and measurements by DSPI. Optical measurement system based on DSPI was built for demonstrate. In order to quantitative determination of the distribution of phase change, several imaging process and pattern evaluation methods are discussed and compared. Phase shifting techniques and phase pattern filter methods also were described in detail. In this paper, some experiments results were given, which clearly demonstrate that that the methods are effective for processing pattern.