Abstract: The problem concerning form finding of the beam(truss)string structures is studied and the method named offloading by steps is put forward in accordance with the mechanical behavior of the structures.The method can be applied to the form finding of the beam string structures stretched at both ends.Without assuming the form of unstrained state,the form of unstrained state corresponding to that of pre-stressed state can be obtained through this method directly.Finally the method proposed is verified by the numerical solution of loading by steps.