In order to study mechanical properties of a carbon fiber grid structure, a type of multilevel grid-stiffened plate was designed, and its mechanical properties were analyzed using theoretical analysis and the finite element method. The grid structure was equivalent to a homogeneous continuous structure. Based on this, an equivalent method for calculation of the grid structure was derived, and the equivalent elastic modulus and the equivalent flexural stiffness of a multilevel grid-stiffened structure were calculated. The results show that the multilevel triangular grid-stiffened structure can improve the anti-buckling ability of ultra-light materials. When the cross-sectional area is the same, the flexural stiffness of the triangular grid is 10% higher than that of the solid structure, indicating that the buckling load of the multilevel grid is higher than that of an ordinary grid.