Abstract：Hydrocarbon compounds in Herbaceous plants play an important role for assessing ecological and environmental changes in cold and arid areas at high altitudes. The alkanes and olefins in Festuca brachyphylla Schult. & Schult. f. from high altitude cold and arid area, Tianshan mountain were analyzed by means of organic geochemical methods， for learning their geochemical characteristics and response to the environment. Results show that, for alkanes in, the carbon numbers range from C16 to C29. The average carbon chain length (ACLAlk) are 17.91~24.49, and the main peak carbon are C16, C18 and C29. For olefins, there are carbon number ranges of C16~C31, the average carbon chain length (ACLOle) of 22.19~26.23，and the main peak carbon mainly C16 and C20. Together, alkanes and olefins in the herb plants exhibit that their overall contents of low carbon number components (carbon number of alkane and olefins are ≤23 and <27, respectively) are relatively higher, and there are even-to-odd predominance in lower carbon number components but odd-to-even predominance in the higher, significantly. By comparing the hot and humid, drought environments, and others, it is found that Festuca brachyphylla Schult. & Schult. f. from high altitude cold and arid area, Tianshan mountain have unique geochemical characteristics, such as with higher content of low carbon alkanes and olefins, lower average carbon chain length (ACL) value, and differentiations of odd-even predominance (OEP) index between of the lower carbon hydrocarbons and of the highers. The average carbon chain length of olefin (ACLOle) value of herbaceous plants with good water supplement are larger, relatively. There is a close positive correlation between the average carbon chain length of alkanes (ACLAlk) and olefins (ACLOle) in Festuca brachyphylla Schult. & Schult. f.. The results obtained provide an important reference for understanding the ecological adaptation mechanism of herbaceous plants in high altitude cold and arid areas and evaluating the impact of environmental changes on ecosystems.