Abstract: Abstract: Phalaenopsis seedlings were treated with the temperature of 40℃(day)/30℃(night) for 0,2,4,6 day respectively,the morphological characteristics and several related physiological indexes in leaves of Phalaenopsis seedlings were determined.The results showed that generation rate of the superoxide free radical(O2-.),the contents of malondialdehyde (MDA),soluble sugar and free prolin were gradually increased with prolonging stress time;During the early 2 day of treatment,soluble protein content ,SOD,POD,CAT activities increased dramatically ,but relative electrical conductivity and chlorophyll content increased slightly.There were no significant difference for relative electrical conductivity and chlorophyll content between during 2 day of treatment and control.The results indicated that the heat tolerance of Phalaenopsis seedlings was improved by enhancing the contents of soluble protein,soluble sugar,free prolin and activities of SOD,POD,CAT.Then the contents of soluble protein,chlorophyll,the activities of SOD,POD and CAT decreased significantly, relative electrical conductivity ascended sharply.