Abstract: In order to meet the needs of developing laser-induced fluorescence (LIF) non-destructive detecting technique, the relationship between chlorophyll fluorescence intensity of cucumber leaf in vivo and laser power was studied by reflectance laser-induced fluorescence (LIF) spectrum analysis technique in this paper. Fluorescence spectrums, which were induced by four kinds of laser power (2.50, 5.00, 7.50, 10.00 mW) of two kinds of center wavelength 473 and 660 nm, respectively, were analyzed in the experiment. Under those conditions, fluorescence intensities of center wavelength 685 and 732 nm for different plant physiology information (chlorophyll content, water content) were calculated and analyzed by MATLAB software. The results showed that there was a very significant linear correlation between fluorescence intensity of each peak position and laser power; chlorophyll content impacted on the relationship between fluorescence intensity and laser power significantly, and a linear correlation between fluorescence intensity gradient of each peak position and chlorophyll content was found. However, that relation insignificantly correlated with water content. Based on those results a mathematical model with chlorophyll content parameter of relationship between fluorescence intensity and laser power was established. The relative square error of prediction of the model was less than 0.2%, and it exactly reflected the relationship between chlorophyll fluorescence intensity and laser power.