Abstract: In this paper double-layer space grids with rectangular shape have been simplified as equivalent sandwich plate and analyzed by the non-traditional theory of plate with three generalized displacements, in which shear deformation is considered. Method for calculating natural frequency of eight types of double-layer space grids has been presented based upon the idea of split rigidity, and the uniform formula has been given out. Natural vibration analysis of those eight types of double-layer space grids has been studied with presented method. The comparison with the results of finite element method is given out. This simplified method is not only simpler but also of higher accuracy, whose error is less than 10 percent in general. As a result, the method in this paper can be a reference for analysis and design of double-layer space grids.