The optical fiber Fabry-Perot (F-P) sensor is simulated and analyzed based on multi-beam interference principle. Then the micro F-P sensor is fabricated by 800nm femtosecond laser mechanism o n the single mode fiber.And the refractive index (RI) response is experimentally t ested.The fabrication parameters can be tunable through controlling the computer .Under different fabricated parameters,the different reflection spectra of the F -P sensor can be formed.According to the theoretical analysis,the fringe contra st of the micro F-P sensor will decrease within the low refractive index region ,and it will increase within the high refractive index regioin (low region:refra ctive index is less than 1.457;high region:refractive index is more than 1.457). The refractive index responses to a variety of different solutions are carried o ut.The results show that the sensitivities of the sensor interference fringe con trast to low and high refractive index solutions are 27.65dB/RI and 3.50dB/RI, respectively.And the experimental results of two refractive index regions bot h e xhibit good linear response.This type of F-P sensor has advantages of high sens itivity,good reproducibility,anti-corrosion,and so on.It is easy to be fabricat ed by femtosecond etching technique.Thus,it has a great potential application in the refractive index sensing field of optical fiber sensors.