A high-efficacy, long-acting formulation of silymarin, comprising silymarin solid dispersion, silymarin-loaded silica nanoparticles, slow-release matrix material and release enhancer, wherein the mass ratio of these components is silymarin solid dispersion:silymarin-loaded silica nanoparticles:slow-release matrix material:release enhancer=1:0.5˜1.25:0.1˜0.3:0.1˜0.3; the drug loading rate of the said silymarin-loaded silica nanoparticles is 51.95%-52.87%; the said silymarin solid dispersion contains povidone K30, soybean lecithin and acrylic resin IV, and the mass ratio between silymarin and other medical accessories in silymarin solid dispersion is silymarin:povidone K30:soybean lecithin:acrylic resin IV=1:1˜3:0.3˜0.8:0.2˜0.5. Compared with the existing formulations, the half life of the high-efficacy, long-acting formulation of silymarin disclosed in this invention is 2.3 times longer while the mean residence time (MRT) of which is 9.94 times longer; when tested in vivo in Beagle dogs, this new formulation of silymarin presents a smoother concentration-time curve and reaches a continuous release for 72 hours. This invention discloses its preparation method.