In this study, morphological and cytological methodologies were applied to preliminarily study the cytogenesis, development and microstructural characteristics of the special morphology of the false dissepiment of Lunaria annua. It was found that the false dissepiment originates from the false dissepiment primordium on the ventral suture. Its development had embryonic stage, extension stage and mature stage. False dissepiments consist of epidermal cells and inner parenchyma cells. At embryonic stage, the false dissepiment shaped hourglassly and the parenchyma cells were rich in brown bodies, while false dissepiments was barbell shaped at extension stage, and the parenchyma cells gradually disintegrated, forming a large cavity. False dissepiments showed a typical linear structure at ripe stage, and the parenchyma cells basically degenerated, leaving only two layers of epidermal cells. The fully mature false dissepiments was nearly round-fan-shape, with epidermal cells arranged in parallel, inclined and vertical ways, and the outer wall was adorned with silver decorations. False dissepiments of Lunaria annua was extremely developed, and developed synergistically with the fruit, belonging to the flattened dorsally type. The formation of highly developed false dissepiment might be related to larger fruits and fewer seeds.