Fiber optical laser interferometry is the main technical scheme for dynamic signal demodulation of external Fabry-Perot interferometer (EFPI) sensors. It has the advantages of high measurement sensitivity, wide dynamic range, and wide measurement frequency range. Based on the measuring principle of an extrinsic Fabry-Perot interferometric sensor, this article presents the demodulation principles, advantages, and disadvantages of presently used phase recovering technologies,and focuses on several new passive demodulation technologies proposed by the author's research group, it mainly solves the problems of existing demodulators which can only measure the sensor with a single cavity length, direct current component removal, and signal demodulation when cavity length changes or even unknown.