By using the layer-by-layer self-assembly technique，the complex membrane was prepared from sodium cellulose sulfate（NaCS）and chitosan，two kinds of polysaccharides with excellent biocompatibility.The process of membrane formation was studied，and the morphology of complex membrane，membrane formation mechanism，and dynamic features of the complex membrane formation were investigated by using scanning electron microscope（SEM），infrared spectroscopy，ultraviolet-visible light absorption respectively.The preparation conditions would affect significantly the formation of complex membrane and the layer-by-layer self-assembly formation was a one-order reaction process under the current preparation conditions.