A projection system with infrared monitoring function, comprising a projection module and an infrared monitoring module; wherein the projection module comprises a projection light source and a projection objective including a first lens group and a light splitting element, wherein the infrared monitoring module comprises a monitoring objective and a sensing chip, wherein the light splitting element is a fixed structure in the projection objective, and wherein infrared light along an optical axis of the infrared monitoring module, before having been deflected by the light splitting element, is coaxial with the optical axis of the projection objective; wherein the projection system further comprises an infrared light source, which is arranged outside of the projection module to emit the infrared light directly to a projection plane without passing through the first lens group; characterized in that the projection module comprises a second lens group, wherein light of the projection light source passes through the second lens group, the light splitting element and, subsequently, the first lens group before being emitted out, the first lens group is movable back and forth whereas the second lens group is a fixed structure in the projection objective, wherein the projection system further comprises a focusing device for driving the first lens group to move back and forth in the projection objective, wherein the infrared light source emits infrared spots which are reflected from the projection plane, pass through the first lens group, and are deflected, by the light splitting element, into the infrared monitor module, and wherein the projection system further comprises an interactive control unit using software algorithms which are adapted to calculate the position and trajectory of the light spots. wherein the projection module comprises a projection light source and a projection objective including a first lens group and a light splitting element, wherein the infrared monitoring module comprises a monitoring objective and a sensing chip, wherein the light splitting element is a fixed structure in the projection objective, and wherein infrared light along an optical axis of the infrared monitoring module, before having been deflected by the light splitting element, is coaxial with the optical axis of the projection objective; wherein the projection system further comprises an infrared light source, which is arranged outside of the projection module to emit the infrared light directly to a projection plane without passing through the first lens group; characterized in that the projection module comprises a second lens group, wherein light of the projection light source passes through the second lens group, the light splitting element and, subsequently, the first lens group before being emitted out, the first lens group is movable back and forth whereas the second lens group is a fixed structure in the projection objective, wherein the projection system further comprises a focusing device for driving the first lens group to move back and forth in the projection objective, wherein the infrared light source emits infrared spots which are reflected from the projection plane, pass through the first lens group, and are deflected, by the light splitting element, into the infrared monitor module, and wherein the projection system further comprises an interactive control unit using software algorithms which are adapted to calculate the position and trajectory of the light spots.