The measurement principles and imaging methods of shearing speckles are introduced in detail. The common shearing imaging modes are discussed in detail and the characteristics of several basic loading methods are discussed and analyzed. The technology has been used in the areas of strain analysis, non-destructive testing and vibration testing etc. widely for the merits of high precision, non-contact, directly measuring strain and insensitivity against ambient noise. The application in the area of non-destructive testing and relative characteristics and advantages of DSSPI are emphasized.