This paper presents a study on layout optimization of truss structures, with a modified stiffness spreading method (MSSM).In this method, background mesh and radial basis functions are no longer used.The bars in a design are divided into two types: real bars and auxiliary bars.Design variables are the all nodal coordinates and the cross sectional areas of real bars, excluding auxiliary bars.The stiffness of the auxiliary bars is kept small during the optimization process and adjusted according to certain criteria.When the length of a bar is short enough, its two end nodes will merge to reduce the complexity of the structure to get a truss layout made up of a few real bars.A way of material allotment is employed to make nodes merge easily.Several test cases are studied.Numerical results are presented which show the effectiveness and efficiency of the proposed method.Finally, concluding remarks are made on the new optimization model and solution algorithm presented.