By the action of xanthine - xanthine oxidase reaction (X+XO) as well as methyl viologen (MV) respectively, it was studied that chlorophyll fluorescence quenching induced by superoxide anion in lettuce (Lactuca sativa L.) chloroplasts. The results showed that the production of superoxide anion increased photochemical quenching(qP) and non-photochemical quenching(qN) evidently. As superoxide dismutase (SOD) was inhibited by sodium diethyldithiocarbamate (DDC) in chloroplasts, qP decreased and qN increased in the quenching of chlorophyll fluorescence induced by X+XO, while the increasing extent of qP was not great and qN rose insignificantly in the quenching of chlorophyll fluorescence induced by MV. When iodoacetamide (JAA) inhibited carbon assimilation, qP decreased and qN increased. Uncoupler NH₄Cl promoted the permeability of across thylakoid membrane proton, which made qP rising and qN decreasing. Under uncoupling conditions, MV raised qP and qN insignificantly. It was analyzed that the producing and scavenging of superoxide anion in time was important to maintain photosynthetic electron transport and to improve transmembrane ΔpH. It contributed to the conversion and dissipation of photon energy absorbed in chloroplasts, and reduced the harm of photoinhibition to a certain extent led by excess photon energy.