In order to meet the needs of low temperature,wide range and highly sensitive temperature measurement,an optical fiber Fabry Perot (FP) cavity temperature sensing technology for low temperature environment is proposed,and the response characteristic of the sensor is studied experimentally.The ultrashort air FP cavity sensor consists of a 0.3mm capillary tube and a single mode optical fiber.The material with high thermal expansion coefficient is used as a reflector of the cavity mirror to improve the temperature sensitivity of the sensor.The temperature sensing principle of FP cavity and the influencing factors of temperature sensitivity are analyzed theoretically,and the influence of different orders on sensitivity is analyzed.The experimental results show that the proposed temperature sensor possesses sensitivity of -2.066 nm/℃ in the range of -40℃ to -10℃.The linearity is 0.9697,with a theoretical resolution of .The sensor has the advantages of small volume,high sensitivity and large measurement range,which has potential application value in the fields of low temperature sensing.