Abstract: Taking Cydonia oblonga Mill as an experimental material to examine the effects of dust on the photosynthesis and chlorophyll fluorescence parameters, three levels of dust treatments during 40 days which comprise non-dust cover（CK）, mild dust treatment （5mg·cm-2）and serious dust treatment（12mg·cm?2）. The results showed that net photosynthetic rate（Pn）, stomatal conductance（Gs）, and transpiration rate（Tr）of the leaves under the dust treatment showed a downward trend with the treatment time. Intercellular CO2 concentration（Ci）showed a trend of increasing first and then decreasing, The maximum light quantum efficiency（Fv/Fm）decreased significantly on the 10th day of treatment, and then gradually increased to the control level with the prolonged treatment time. For two dust treatments, maximal fluorescence（Fm）, non-photochemical quenching under stable state（NPQ_Lss）, potential activity（Fv/Fo）and photochemical quenching under stable state（qP_Lss）increased with treatment time, but minimal fluorescence（Fo）decreased with treatment time .These results indicated that the non-stomatal inhibition had a significant on the photosynthetic rate greater at the beginning, the dust stress reduced the primary photochemical efficiency of PSⅡto cause photoinhibition. In later stage, Cydonia oblonga Mill promoted the efficiencies of photosynthetic electron transport due to increase such as qP_Lss，Fm and NPQ_Lss. On the other hand, Cydonia oblonga Mill increased non photochemical dissipation to protect the photosynthetic organs.

Key words: Cydonia oblonga Mill, Dust stress, Net photosynthetic rate, Intercellular CO2 concentration, Maximum light quantum efficiency