A spherical thermistor, an accurate temperature sensor, is employed as an air velocity sensor in this work. The measuring principle is derived and the effects of the insulation layer, air temperature, natural convection and thermal radiation are discussed. Two different correlation relations for velocity measurements are proposed based on theoretical analyses and experimental calibrations. Experiments have shown that spherical thermistor is a good velocity sensor for speed between 0.1-2.5 m/s at room temperature and the insulation layer hardly influences the accuracy of the thermistor used in the present work. Modification on correlation can even further improve measurement accuracy. Since the thermistor is small and cheap, it is possible to apply this method to multi-point velocity measurement with a low disturbance to the flow field. A spherical thermistor, an accurate temperature sensor, is employed as an air velocity sensor in this work. The measuring principle is derived and the effects of the insulation layer, air temperature, natural convection and thermal radiation are discussed. Two different correlation relations for velocity measurements are proposed based on theoretical analyzes and experimental calibrations. Experiments have shown that spherical thermistor is a good velocity sensor for speed between 0.1-2.5 m / s at room temperature and the insulation layer not influences the accuracy of the thermistor used in the present work . Modification on correlation can even further improve measurement accuracy. Since the thermistor is small and cheap, it is possible to apply this method to multi-point velocity measurement with a low disturbance to the flow field.