A new type of fiber optic glucose biosensor based on fluorescence quenching has been designed and its properties have been studied. Glucose can be oxidized by oxygen when glucose oxidase are used as the catalyst, therefore, the concentration of glucose can be measured by detecting the consumption of oxygen. For the detection of oxygen concentration, the ruthenium(II) complex, Ru(bpy)3Cl2, were used as the fluorescence indicator and its fluorescence lifetime were detected by lock-in technology. The detecting range of the sensor is 50-500 mg/dl and its response time is 30 seconds, showing that this kind of sensors is possible to be used in clinical diagnosis and detection.