To investigate the response of photosynthetic apparatus to UV-B radiation,we investigated the changes of chlorophyll fluorescence parameters under artificial simulated low UV-B radiation treatment(2.4 μW/cm²),that including Chl a fluorescence transients induced dynamic curve,F₀,F_m,the parameters of PSⅡ reaction center activity(ABS/RC,TR_o/RC and ET_o/RC) and performance index (PI) in leaves of Glycyrrhiza uralensis,by using the pocket PEA.The results suggested that:(1)UV-B mainly influenced the acceptor side of PSⅡ system rather than its donor side because of the O-J-I-P chlorophyll fluorescence induction curves didn’t change by low level UV-B radiation.(2)The results of F₀,F_m and F_v/F_m indicated that UV-B radiation inhibited the openness of reaction center and blocked the transporting of electron from Q_A to Q_B,and that was confirmed by the decreasing of PI_abs and PI_total.Thus,low level UV-B radiation influences photochemical or non-photochemical reaction beyond Q_A as result of reduced electron transportation efficiency from Q_A to PQ.