Abstract: Experimental research on form finding of beam string structures is carried out in order to verify offload-by-steps method, and more importantly, to study the application of the method in engineering practice. The scale of model is 1/20, and the stretching pattern is the same as that of practical engineering. Comparisons of internal forces and deformations corresponding to unstrained and pre-stressed states of the model are made between experiment and calculation. The following conclusions are drawn: Firstly, offload-by-steps method can be applied to engineering practice without assuming the form of unstrained state and repeating calculatins. And the form of unstrained state corresponding to that of the pre-stressed state can be obtained directly. Secondly, the internal force of beam string structures in pre-stressed state can be obtained easily by using the statically determinate calculation model in offload-by-steps method, which can guide design effectively. Thirdly, the method for estimating the cable tension balancing the deadweight of beam string truss can be applied to engineering practice.