The invention discloses a method for preparing a classical swine fever (CSF) vaccine by using a cell microcarrier suspension culture system, which comprises the following steps of: (1) inoculating cells for preparing the vaccine to a carrier tank containing culture solution and a microcarrier, and uniformly mixing the cells and the microcarrier to make the cells attached to the microcarrier; (2) when the concentration after cell proliferation is 5 to 40 times of the initial inoculation concentration, inoculating CSF virus (lapinized virus) to the cells according to multiplicity of infection (M.O.I.) of the virus of 0.01-1 and reproducing the virus; and (3) mixing prepared virus liquid, adding an appropriate freeze-drying protective agent, fully and uniformly mixing, quantitatively packaging, and freeze-drying to obtain the CSF vaccine. The CSF vaccine produced by the method has the advantages of high density of cultured cells, continuous culture, high yield of the virus, high immune effect, high safety, complete immune protection on attack of violent CSF, and the like.