Abstract: The portable photosynthesis instrument CIRAS-3 is often used in the field. Improper operation and use may lead to unstable measurement data or excessive deviation, which will reduce the test efficiency and affect the progress of experimental research. In order to let the beginners to master, quickly, the correct operation method of CIRAS-3, to operate properly and get effective photosynthetic data, according to the experience, the testing principle, usages, precautions, maintenance and common problems of CIRAS-3 were summarized, so as to provide an effective reference and help for users, and improve, effectively, the use efficiency of the photosynthesis instrument.