A stage lighting optical system includes a light source assembly from which condensed light can be emitted, an object assembly, and a zoom lens assembly, which are located in a same primary optical axis direction. Light from the light source assembly is cast by the object assembly and the zoom lens assembly. The object assembly includes an object for beam mode assembly and an object for gobo mode assembly that can be switched with each other and enter to the primary optical axis. The light source assembly can move forward or backward along the primary optical axis with respect to the object assembly. When the light source assembly moves forward to a first position with respect to the object assembly, the beam mode assembly is switched to the primary optical axis. When the object for beam mode assembly moves backwards to a second position with respect to the object assembly, the object for gobo mode assembly is switched into the primary optical axis.