Based on an asymmetric dual-core photonic crystal fiber,a temperature sensor is proposed.Liquid ethanol as the thermos-sensitive media is filled in one of the fiber cores.According to the directional coupling effect of dual-core fiber,temperature measurement is realized by detecting the central wavelength of the directional coupler.The imaginary-distance beam propagation method is used to study the relation between fundamental mode effective refractive index and temperature.Results show that the dual-core fiber has good temperature sensing characteristics,and the temperature sensitivity reaches 3.73 nm/ ℃ when the temperature ranges from -20 ℃ to 70 ℃.The beam propagation method is used to simulate the transmission characteristics of LP01 mode.Results show that the wavelength corresponding to the main maximum in the transmission spectrum remains constant at the same temperature when the length of the fiber is 0.5 to 1.5 times of the coupling length,and the sensor has a large fabrication tolerance.