The space grid homogenization theory used in space grids design was adopted to homogenize the trusscored metal sandwich plates.The bending stiffness and equivalent shear stiffness of the homogenized plates were obtained by using Reissner sandwich theory and the space grid homogenization method respectively.The formulae of the natural frequencies of four typical trusscored metal sandwich plates were then derived by using the Method of Split Rigidities (MSR).The frequencies of trusscored metal sandwich plates obtained by the formulae are in good agreement with those by finite element method.Moreover,the influence of structure parameter of the unit cell on the natural frequencies was analyzed.Optimization with the goal of a maximal first natural frequency was performed by optimizing the height of truss core and the crosssectional area of the truss.The trusscored metal sandwich plates after optimization have a much higher first frequency compared with the original design.