Fluorescence has been widely used in biological research and clinical diagnosis. One challenge facing the rapid growth of fluorescence application is the inability to make comparable fluorescence intensity measurements during a long period of clinical study and across laboratories. We propose a method to implement system-independent fluorescence intensity calibration in fiber-optic fluorescence spectrometer systems. This method is based on a National Institute for Standards and Technology traceable standard light source for system spectral response calibration, and a fluorescence reference standard for fluorescence intensity calibration. Human skin in vivo and a fluorescence phantom made of fluorescent microspheres were measured with two different system configurations and at different probe-sample distances. Experimental results showed very good agreement with theory after system-independent fluorescence intensity calibration.