Abstract: Change of water physiology of Cymbidium hybridum growth in different media and its moisture condition were studied.And the media water content(MWC),leaves water content(LWC) and water potential(WP),as well as stoma conductance(SC),transpiration rate(TR),chlorophyll content(CC) of leaves and superoxide dismitase(SOD) catalase activities(CAT),peroxidase(POD),relative permeability(RP) were tested.The results showed that Sphagnum(SP) medium had a higher water holding capacity than peanut hull mixed with sand.The critical MWC were about 15.86%~12.32% in SP media,and 16.42%~12.29% in PH/Smedia.The critical LWC was about 87.41%~80.31%.The change of CC slowly response to water deficiency,for which,changed more slowly than that of WP and LWC.The RP increased rapidly during the end of the water treatment.The change of the activities of SOD,CAT,POD,and the content of MDA and PRO were so complicated that could not be the practical index of water deficiency.The LWC and LWP were the practical parameter to determine water deficiency of Cymbidium hybridum.