Fiber Bragg Grating （FBG） thermal flow sensors are only suitable for gas flow currently. In order to expand its application field， a new FBG thermal flow sensor that can be used for liquid flow measurement is designed. A heating ceramic sheet is used to provide heat at a constant power for the FBG thermal flow sensor. Different flow of liquid takes different heat when flow through the sensor. By detecting the change of FBG central wavelength， the temperature change of the sensor can be measured， and then the liquid flow can be deduced. Through temperature sensor test experiment and flow sensor test experiment， it is verified that the designed sensor can be used for liquid flow measurement. The experimental results show that the flow measurement range of the sensor is 40.575~550.664 L/h.