In order to improve the precision of small measure equipment, the manuscript presents a structure of common aperture, long wave infrared rays/laser dual-mode measure equipment. Then an optical system is designed to match the system’s needs. The long wavelength infrared imaging system and the laser receiver, laser emission system use the same protect window, the far infrared imaging system and the laser receiver use the same aperture and reflector, in this way the size of optical system is reduced. The volume of the whole optical system is 450 mm×164 mm×164 mm, coincident with the requirement of small and light. At last, analysis the performances of each optical systems by the software, the modulation transfer function of the far infrared imaging system is above 0.23 at 30 lp/mm, the optical path difference of the laser receiver is smaller than 1/4 wavelength, the spot diagram of laser emission system is smaller than 10 μm, all of them can match the project requirement.