Abstract: Path analysis is a multivariate statistical technique put forward by geneticists Sewall Wright in 1921,based on the surface direct correlation decomposition between dependent and independent variables,to study the direct and indirect importance of independent variable on the dependent variable,so as to provide reliable basis for statistical decision.Plant photosynthesis and transpiration is one of the most important physiological activities,they have close relationship with environmental factors such as light,temperature and humidity,at the same time,the photosynthesis is the main factors of plant yield components,to study the relationship between the environmental factors and photosynthesis,transpiration could help to enhance the plants photosynthetic capacity,so as to achieve the purpose of increasing production.The effects of environment factors such as photosynthetic,active　radiation,air humidity,air temperature,carbon dioxide on photosyn thesis and transpiration characters of Elymus sibiricus in enough moisture were studied using stepwise regression analysis and path analysis,decision factors between the environmental factors and transpiration rate,net photosynthetic were calculated.The transpiration rate,net photosynthetic rate were test using normal distribution before path analysis.The analysis results are examined using significance test until each variables in regression equations reached significant level.Different point of view such as correlation,partial correlation analysis is using to study the correlation between photosyn thesis,transpiration characters and the environment factors.The results indicated that carbon dioxide,temperature,air humidity have inhibitory effect on net photosynthetic rate while carbon dioxide,air humidity promote transpiration rate.

Key words: Elymus sibiricus, photosynthetic, transpiration rate, environmental factors, stepwise regression analysis, path analysis, decision coefficient