A fluorescence intensity analyzing and fluorescence image synthesizing system and method are disclosed. The first fluorescence intensity detection device successively detects the plurality of first fluorescence intensities according to the first timing and the second fluorescence intensity detection device successively detects the plurality of second fluorescence intensities according to the second timing, and then the picture processing device analyzes the first and second timings and synthesizes the first and second fluorescence intensity ranges into the synthesized picture according to the fluorescence intensities, whereby the image processing technology may be used to calculate the fluorescence target range and thus mark the fluorescence target range.