Abstract: Abstract: Studied the changes of physiological Indexes ,such as RWC(relative water content), CAT activity,MDA content,PRO content,of tall fescue “Houndog5” under the optimum temperature (15℃,25℃) and high temperature (35℃, 45℃). Compared with the temperature of 15℃, the results showed that the RWC and the CAT activity decreased significantly, MDA and PRO content increased obviously under high temperatur,then cell membrane-lipid peroxided,membrane structure be destroyed,physiologic function disordered and resistance decreased,these were main reasons of tall fescue oversummering hard and get ill easily.The correlation analysis showed that RWC and CAT had significant positive correlation(r>0.95), RWC, CAT and MDA, PRO had significant impositively correlation(r> -0.95), MDA and PRO had significant positively correlation(r>0.95). Therefore,to select RWC and PRO determined easy as important parameters of breeding heat resistant variety will reduce lots of workload and improve work efficiency.