Abstract: The main purpose of semi-spring contact model is to judge anddescribe the contact status, and then to calculate the contact force betweenblocks. Contact blocks are divided into mother block and son block.Semi-spring is located in mother block, and formed by indenting the vertexof block to mother face, while target face lies in the son block. Accordingto the geometry relationship between semi-spring and target face, thecontact force could be obtained directly. There is no need to waste a mountof time to judge the contact type and calculate contact area between twoblocks. The model could calculate the progressive failure of geological bodyunder the conditions of quasi-three-dimension, and some numerical casesabout slope failure are shown to proof its accuracy and reliability.