Cable-stayed truss with triangular cross-section has been adopted in this paper.It has great unloading effect and is more reasonable when bearing loads.The cable-stayed space truss model was built by ANSYS10.0 software.The analysis is performed for vertical displacements of nodes after applying various prestressing force to stayed cables.Then the vertical displacements of nodes are fitted by MATLAB7.0 software and the curve-fitting polynomials are obtained,which overcomes the disadvantage that only nodal analysis was performed before.The analysis results show that applying prestressing force to stayed cables can control the vertical displacements well.