To reveal the complex relationship between ecophysiological indexes and environmental factors of Populus simonii and find out the important indicators. Under three different conditions of adequate soil water, medium drought and severe drought, the impact of water stress on physiological growth change of Populus simonii was studied. Under the condition of manual control, net photosynthesis rate (Pn) stomatal conductance (Gs) and their changes were analyzed in response to active photosynthetic radiation and CO2 concentration; Under medium drought condition, the complex interaction between different indexes were revealed through direct correlation and integrated correlation analysis. The basic ideas of comprehensive correlation analysis were: (1) All the principal components of the variable group Y1, Y2,…, Yn executed vector synthesis according to proportion of variance contribution rate, and formated variable F1, similarly, from the main components of the variable group X1, X2,…, Xn, variable F2 was formated, then seek the F1 and F2 correlation coefficient to act as the integrated correlation coefficient R of variable group X and variable group Y. (2) Integrated correlation coefficient R was decomposed into the correlation coefficient Rij between Xi and Yj, Rij also divided into direct and indirect correlation coefficient between Xi and Yj, thus revealed the complex relationships. Important findings: (1) Under three different soil water content, the basic physiological and comprehensive indicators of Populus simonii, such as the net photosynthetic rate (Pn), transpiration rate (Tr), respiration rate (R) and total water consumption, were significantly different, which indicated that water stress had an important impact on growth of Populus simonii.(2) In manual control experiment net photosynthetic rate (Pn) in Populus simonii leaves increased with the increase of photosynthetic active radiation (PAR) under average atmospheric CO2 concentrations. When PAR was 0-500μmol?m-2s-1, Pn was the fastest-growing. This result indicated Populus simonii has better adaptability to strong light. Stomatal conductance (Gs) increased with the PAR increase. Pn increased with the CO2 concentration increase in certain PAR (1500μmol?m-2s-1) conditions, showing that the current atmospheric CO2 concentration could not provide sufficient raw materials to meet photosynthesis of Populus simonii, and improving the concentration of CO2 could significantly increase the net photosynthetic rate of Populus simonii.(3)The results of direct correlation analysis and comprehensive correlation analysis showed that active photosynthetic radiation (PAR), CO2 concentration and air temperature (Ta) had a remarkable influence on physiological growth of Populus simonii in moderate drought. Important indicators that can reflect ecophysiological characteristics of Populus simonii were as follows: water consumption, transpiration rate (Tr), respiration rate (R) and net photosynthesis rate(Pn). Physiological indicators and environmental indicators were highly correlated. In conclusion, changes in physiological growth of Populus simonii were the combined inflluence of soil water condition, active photosynthetic radiation,CO2 concentration and air temperature and its physiological growth characteristics should be studied by multi-index analysis.The comprehensive correlation coefficient analysis is scientific and rational and is superior to the direct correlation analysis.It is worthy of study and popularization.