Abstract: Web buckling behaviors in web lattice-enhanced foam-sandwich structures under in-plane compression are investigated through finite element analysis (FEA) under static flat compression to study the effects of such factors as web space, web height, and elastic modulus of the foam core. To estimate the critical buckling load, a half-wave number foundation coefficient is proposed to simulate the resilient support to the web based on Winkler foundation model. The theoretical method and formula for buckling behaviors are obtained by Ritz method. Analysis shows that web buckling behaviors due to the existence of foam are far different from those which occur when it is absent. With the increasement of web height, the critical buckling load increases steadily and the buckling mode changes to multi-peak wrinkling. The support action of the foam plays the leading role in controlling the web stability, if web space and height are large. The critical buckling load from the theoretical method is in close agreement with the result from FEA and from experiments as a whole.