1. A fluorescence intensity analyzing and fluorescence image synthesizing system, comprising: a first fluorescence intensity detection device, successively detecting a plurality of first fluorescence intensity ranges according to a first timing, each corresponding a first timing point; a second fluorescence intensity detection device, successively detecting a plurality of second fluorescence intensity ranges according to a second timing, each corresponding to a second timing point; and a picture processing device, communicatively connected to the first and second fluorescence intensity detection devices, and comprising: a receiving module, receiving the first timing and the first fluorescence intensity ranges form the first fluorescence detection device, and the second timing and the second fluorescence intensity ranges from the second fluorescence detection device; a timing analyzing module, analyzing the first and second timings and an identical time ranges between the first and second timings, respectively; a picture synthesizing module, synthesizing the first and second fluorescence intensity ranges according to fluorescence intensity at the same timing point of the identical time ranges into a synthesized picture; and a picture processing module, subjecting the synthesized picture to an image process to calculate a fluorescence target range and mark the fluorescence target range.