The invention discloses an LED circular disc type lens optical system. A lens is a circular disc type lens; an LED light source is arranged at the inside end of the lens; a first section of a free curved-surface cambered surface is arranged above the LED light source; light emitted by the LED light source generates total emission through the first section of the free curved-surface cambered surface; an inclined second section of a reflecting surface is arranged under the first section of the free curved-surface cambered surface; the second section of the reflecting surface is stepped; and each step plane of the second section of the reflecting surface corresponds to the first section of the free curved-surface cambered surface. According to the LED circular disc type lens optical system disclosed by the invention, the LED light source and a plurality of groups of free curved-surface total-reflection surfaces are used to perform a delicate optical structural design, so that various light-emitting effects can be realized without an extra LED, and therefore, production cost of a signal lamp is reduced, and a creative light-emitting effect of the signal lamp is realized.