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, the first fluorescence intensity detection device detects a fluorescence intensity of a fluorescence in a testee excited by irradiating an exciting light source; 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, the second fluorescence intensity detection device detects the fluorescence intensity of the fluorescence in the testee excited by irradiating the exciting light source; 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 from 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 3D 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; wherein timing point range of the second timing for detection of the second fluorescence intensity range and timing point range of the first timing for detection of the first fluorescence intensity range have to be partially overlapped; and a wavelength range of the excited fluorescence detected by the first fluorescence intensity detection device and the wavelength range of the excited fluorescence detected by the second fluorescence intensity detection device are the same.