Through observing the responses of photosynthesis in leaves of broad bean grown under natural conditions to light and CO(2) using a portable photosynthetic analyzer LI-6400, the following findings were obtained. (1) Observing the response of photosynthesis to light using a leaf without being induced by light might lead to an artifact that photosynthesis was not saturated even under full sunlight. (2) The calculated saturating light intensity of photosynthesis by some empirical equations was much lower than actual value obtained by observing. (3) During observation of photosynthetic response to CO(2), each step of changing CO(2) concentration should be accompanied by a match step of the photosynthetic analyzer, otherwise, there will be substantial deviations in the results obtained. (4) Observing photosynthetic response to CO(2) at non-saturating light might lead to an underestimation of leaf photosynthetic capacity.