Abstract: In order to learn about some basic biological characteristics of Castanopsis hystrix,one dominant or constructive tree species in the subtropical evergreen broad-leaved forests,effects of radiation,temperature and water stress on several parameters of chlorophyll a fluorescence in detached leaves of(C.hystrix)were studied.The results showed that:(1)The F_v/F_m(maximal photochemical efficiency of PSⅡ)in leaves of C.hystrix only decreased 6.1% after the treatment by strong light intensity,comparing to F_v/F_m in leaves of Psychotria rubra,a shade-tolerant shrub,which had a stronger inhibition((17.17%))under same light stress,suggesting C.hystrix had favourable adaptation to sun environment;(2)Little decrease in ETR(electron transport rate)with consistent F_o in the detached leaves treated by 4℃ for 72 h indicated the insensitivity to short-time chilling;(3)No significant difference in F_v/F_o and F_v/F_m demonstrated little influence on PSⅡ potential activity and maximal photochemical efficiency of(PSⅡ)by chilling treatment in the dark;(4)A significant decrease in ETR,F_v/F_m and F_v/F_o((p<0.01))and the great increase in F_o(p<0.05)by hot shock at 40℃ to the leaves for 2 h and 4 h,respectively,showed potential damage to its photochemical reaction center;(5)Increase in F_o by(44.7%)and decrease in F_v/F_m by 22.4% and F_v/F_o by 54.4% in the leaves with water detect simulated by PEG after one-day treatment independently reflected inhibition of the potential efficiency suggesting(intolerance)to drought for C.hystrix.