Membrane is a widely used structure in aerospace engineering, but its modal characteristics in the vacuum and air environment are quite different. Due to the limitations of test equipment and simulation modal identification methods, there is less literature including both simulation and experiment of membrane structures in both vacuum and air environments simultaneously, and there are few comparisons between the modal identification methods of the above simulation and experiment. Therefore, a low vacuum experiment device was introduced firstly. Then the first four modals of a membrane identified by the Lancoz method and a stochastic subspace identification (SSI) method were compared. The results show that the two methods have fine consistency. Moreover, these results were compared with the experiment results. The simulation and experiment have a good correspondence in the vacuum environment, but in the air environment the frequencies are different, and the deviation decreases as the thickness of the membrane increases. Finally, the effects of the number of observation points and the amplitude of the exciter on the modal identification results were discussed through simulation analysis.