Abstract: DEM(digital elevation model) has a wide variety of application in GIS and CAD.It is the basic model for generating three-dimensional terrain feature.Generally speaking, there are two methods for building DEM.One is based upon disordered points digital terrain model with features of fast speed and low precision.The other is built upon triangular digital terrain model with the peculiarities of slow speed and high precision.Compositing the advantages of the two methods,an algorithm for generating DEM with disordered points is presented in the paper.When interpolating elevation, it can create a trangle which includes interpolating point and the elevation of the interpolating point can be got with the triangle. The method has the advantage of fast speed,high precision and requirement,for little memory.