The invention provides an optical system of a star simulator. The optical system of the star simulator comprises a first lens, a second lens, a third lens and a fourth lens. The first lens, the second lens, the third lens and the fourth lens are arranged on optical axes on the same horizontal light path in turn. After passing through the first lens, the second lens, the third lens and the fourth lens, light emitted by a lighting system is emitted in parallel. The first lens is a negative lens and made of BF11 glass. The second lens is a positive lens and made of TF3 glass. The third lens is apositive lens and made of the TF3 glass. The fourth lens is a negative lens and made of the BF11 glass. According to the optical system of the star simulator provided by the invention, the optical system having the advantages of small distortion, low wave aberration, low ratio chromatism, uniform confusion disc, high imaging quality, long focal distance and large view field projection is composedof the four lenses; and the imaging precision of the optical system of the star simulator is increased.