It is nearly impossible to carry out prototype experiments of large deployable space antennas because of their large dimensions. To solve this problem, a performance prediction approach is proposed in this paper. The prototype’s working performance is predicted by the scale model of the large deployable antenna. Based on this method, the natural frequency of the ring tension truss deployable antenna working in space is studied. The effect of the structural parameter distortion is taken into consideration by similarity criteria, and a similarity experimental formula of structural natural frequency is obtained. Four finite element models are established to validate the correction of the prediction method. The simulation results show that it’s valid for the prediction method to analyze the prototype in space, and it can be applied to promote the design, and performance prediction of the large deployable antennas.