Ultra-low temperature pressure sensors refer to the pressure sensor that can work normally in the temperature range of 4~110 K. Nowadays, liquid hydrogen and liquid oxygen are widely used as fuels in space vehicles, which puts forward requirements of pressure parameter measurement in ultra-low temperature environment. At present, electronical sensors have been reported to measure pressure in ultra-low temperature environment. However, electrical sensors contain electromagnetic interference and potential safety hazards, making them unable to work in a harsh environment. Due to advantages of intrinsic safety, high sensitivity, immunity to electromagnetic interference, small volume, light weight, fiber optic sensors have been widely used in various fields of physical quantity measurement. The structure of the extrinsic Fabry-Perot interferometer is naturally suitable for pressure measurement. Optical fiber extrinsic Fabry-Perot interferometer pressure sensors are mainly divided into two types: diaphragm-based type and diaphragm-free type. Diaphragm-free fiber pressure sensors can be only used to measure gas pressure and the sensitivity is greatly affected by temperature. For the diaphragm-based type, to measure pressure in ultra-low temperature environment, a pressure sensor must have a robust structure at ultra-low temperature and the material of the diaphragm needs to be resistant to ultra-low temperature. Since no other materials are introduced, the all-silica diaphragm-based pressure sensor has advantages of high mechanical strength and small size. One method is selective etching of the fiber core to form a micro-hole. Compared with chemical etching method, fs laser micromachining is a safe method to fabricate the air cavity and the thin diaphragm due to high precision material processing capability. Optical fiber sensors have been used for temperature measurement at ultra-low temperature, which proves that pure quartz is resistant to ultra-low temperature. In this paper, for the measurement of pressure at ultra-low temperature, a micro optical fiber extrinsic Fabry-Perot interferometer sensor is proposed and experimentally demonstrated. The end face of a single mode fiber is inscribed by a femtosecond laser to form a micro-hole. Then the single mode fiber is spliced to a non-core fiber to form a sealed Fabry-Perot cavity. The micro optical fiber pressure sensor is fabricated by cleaving and grinding the non-core fiber. By femtosecond laser micromachining, micro-holes with different apertures and diaphragms with different thicknesses can be processed to obtain pressure sensors with different sensitivities and pressure measurement ranges. The test system is shown in the figure below. Experiment results show the sensor proposed in this paper exhibits good linearity within a pressure range from 0 to 5 MPa at -196℃, and the cavity length-pressure sensitivities during the process of pressure increasing and decreasing are 110.33 nm/MPa and 110.68 nm/MPa, respectively. The proposed sensor can meet the pressure measurement requirements in an ultra-low temperature environment.