The invention discloses a preparation method of a self-cleaning glass with a GST compact crystal grain structure, which includes steps of (1), arranging a first film coating reaction device in a temperature zone at 635-640 DEG C of a tin slot; and arranging a second film coating reaction device in a temperature zone at 620-630 DEG C of the tin slot; (2), delivering the first raw material gas in the first film coating reaction device to perform the film coating reaction on a glass substrate in the tin slot; (3), delivering the second raw material gas in the second film coating reaction device to perform the film coating reaction on the film coating glass substrate in the tin slot. The method applies a double-layered film refractive gradient to reduce the refractive index of the composite film layer; the large-area film coating uniformity is good, and the cost is low.