Abstract: The X-5 strain producing thermotolerant alkaline lipase was isolated from rich oil soil. It was identified as pseudomonas sp. according to morphologic observation, physiology and biochemistry experiments and 16S rDNA sequence analysis. The optimal growing conditions were studied by single-factor experiment. The result showed that the following were the optimal growing conditions of X-5:the optimal growing temperature was34℃ and the optimal growing pH was 8.0. The growing curves showed that logarithmic phase started after 6hours. It was in the stationary phase from 26³8 hours, then after 38 hours decline phase started. The study about enzymatic properties showed that the optimal temperature and pH were 60℃ and 8.5 respectively. It remained 60 percent enzymatic activity in 70℃ for one hour. K+、Na+could improved enzymatic activity, however, other ions such as Ca2+, Mg2+, Zn2+, Fe2+, Cu2+and Mn2+ had opposite influence.