Additive-manufacturing process has substantially promoted the development of lattice structure and makes it possible to fabricate complex lattice sandwich structures. In-plane compression load always appears in engineering, such as in the primary structure of spacecraft. In order to reveal potential engineering application in future, this paper focuses on the lat-tice sandwich plate that is fabricated by additive-manufacturing and subjected to in-plane compression. Firstly, five failure modes are proposed for lattice sandwich plate under in-plane compression, including Euler buckling, shear buckling, face sheet dimpling, face sheet wrinkling and face sheet crushing. Secondly, an optimization method is proposed to obtain the optimum sizes, including the panel thickness, the length of rod, the size of rod cross-section, the inclined angle of rod and the wideness ratio of cell. Then, the in-plane compression experiment is operated after measuring the geometrical imperfection of the specimen by the optical microscope. Numerical method is adopted to illustrate the effect on failure behaviors caused by the imperfections of struts, face sheets and global shape. By introducing these imperfection, numerical result can be well agreed with experimental result and explain the failure mechanisms mostly derived from the radius imperfection for the struts.