In this paper, spring analogy method for dynamic unstructured grids is studied. The stiffness of the springs in the modified vertex spring analogy is analyzed. The standard method is improved in consideration of preventing extrusion, torsion stiffness coefficient and the boundary effect. Applications of the improved spring analogy method to 3D-grids generation show that the new method greatly upgrades the deforming ability and the quality of the grids. Coupled with 3-D ALE Euler solver this dynamic unstructured grid method is applied to simulating transonic unsteady flow about a rectangle rigid wing and a high-aspect ratio sweepback wing. The computation results are in good agreement with those of the literatures and experiments.