The water-soluble fluorescent carbon quantum dots (CQDs) with glucose as a carbon source and polyethylene glycol (PEG) as dispersant and surface modifier, were synthesized in aqueous medium by microwave irradiation and hydrothermal methods respectively in order to explore the preparation of CQDs. The effect of reaction temperature, time, PEG/glucose molar ratios and pH value on the fluorescence properties of CQDs were discussed by using orthogonal experiment method. The results suggest the influence factors from main to secondary are the reaction time, reactant mole ratio and reaction temperature. The reaction temperature 180 ℃, reaction time 2.5 min, PEG-200/glucose molar ratio 6∶1 and pH=9 are the optimal condition of microwave synthesis of CQDs. And under the resulting optimized conditions, the optical properties of CQDs obtained by the hydrothermal and microwave irradiation two methods are compared preliminary. The results show that the performance of carbon quantum dots prepared by hydrothermal method is superior to that of microwave method. But the two preparation methods of fluorescent CQDs have both good fluorescence properties. They can be used in the field of fluorescent labeling.