Abstract: Based on the digital image processing and analysis technology,the microstructure parameter of granular soils was computed from the photos taken from the surface of the model box in granular soil model tests.Firstly,some requirements were proposed for the operation in test to make sure that granule and hole could be differentiated approximately by a threshold of magnitude of the image.Then,by use of morphologic watershed segmentation as well as the image pretreatment steps such as smoothing,region marking and region merging,the edge image was acquired.The coordinates of granular edge and other necessary data could be gained by scanning this image.Based on the above data,a basic structure was prompted,from which the parameters about the area and shape of granules,the parameters about the area and shape of holes,and the parameters about the contact relation of two granules could all be computed.Finally,the limitation of the method was discussed and a simple example was given.