To investigate the effect of water stress on chlorophyll fluorescence parameters of tea seedlings, Longjing tea seedlings were selected for water stress experiments. The slope fluorescence index SFI was proposed to assess the drought stress condition of tea seedlings by using chlorophyll fluorescence imaging technique, and the polar difference R of the mean gray value at the same time within 1~8 days was calculated, and the relative error of R was used to determine the stable time range of the polar difference, and the correlation model between the change of slope of each point on the curve and the number of days of stress was established in this interval. The correlations between the slope fluorescence index SFI, dynamic fluorescence index DFI, photosynthetic function index PFI, and fluorescence decay ratio Rfd and the number of days of stress were analyzed and compared. The results showed that there were no significant correlation between Rfd, PFI and days of stress; and there were correlation between SFI, DFI and days of stress. The correlation between SFI and days of drought stress (coefficient of determination R2=0.94) was significantly higher than that between DFI and days of stress(R2=0.60) when the ROI of the region of interest was 50×50pixel. The use of SFI to assess the drought stress status of tea tree seedlings has higher accuracy and provides a reference for monitoring plant growth in modern agriculture.