Abstract: In order to explore the mechanism of Pseudomonas fluorescens,in this paper,the effects of four Pseudomonas fluorescens strains on net photosynthetic rate,transpiration rate,stomatal conductance,intercellular carbon dioxide concentration,saturated water vapor pressure and growth index of Cerasus seedlings were studied by using portable CIRAS-Ⅱ photosynthetic system.The results showed that compared with the control,the 3-7-2 treatment significantly increased the net photosynthetic rate（19.1%）,transpiration rate（40.0%）,stomatal conductance（48.3%）,and the net growth of stem diameter was extremely significant,it was 121.7% higher than the control,and the net growth of plant height was significantly higher than that of the control.Treatment 3-8-2 significantly increased net photosynthetic rate（20.3%）,transpiration rate（40.0%）,stomatal conductance（47.6%）,saturated vapor pressure（4.7%）,net growth of plant height,the net growth of stem diameter,leaf width and leaf length were significantly higher than those of the control.Therefore,the growth-promoting effects of strains 3-7-2 and 3-8-2 were more significant.