Due to the quantum confinement effect of graphene quantum dots (GQDs), the fluorescence properties of the GQDs can be adjusted by changing the size of the GQDs. We can obtain better fluorescence properties of the GQDs by varying the preparation conditions. GQDs were prepared by the pyrolysis method. To obtain GQDs with excellent fluorescence properties, the effect of different pyrolysis times and pH values on the properties of GQDs were studied. Fourier infrared spectroscopy, x-ray diffraction, transmission electron microscope, and fluorescence spectroscopy (PL) were used to characterize the morphology, structure, and fluorescence properties of GQDs. The experimental results show that with the increase of pyrolysis time, the carbonization of citric acid intensifies, the size of GQDs increases, the fluorescence peak of GQDs broadens, and the dependence of fluorescence emission increased gradually. Fluorescence property changes with the pyrolysis time, the fluorescence property is optimal with the pyrolysis time of 30 min, and the suitable pyrolysis time will cause the citric acid sufficient reaction to produce the maximum yield of GQDs. Besides, GQDs fluorescence properties are also affected by the acid-base environment. The fluorescence of GQDs solution has the strongest in an alkaline environment and quenched in an acidic environment.