This paper reports a high sensitive refractive index composite fiber sensor comprising the polymer micro-fiber fabricated by directly drawing method from poly(methyl methacrylate) colloid. Through the evanescent wave coupling method, the whole sensing system was built by means of micro-manipulation under microscope. The dip wavelength in the measured spectrum caused by the models interference shifted obviously when the surrounding refractive index changed. The approximate linear relationship between surrounding refractive index and dip wavelength shift was obtained experimentally. The measurement sensitivity have been demonstrated up to 1490nm/RIU with the surrounding refractive index ranging from 1.3333 to 1.3403 by using the polymer micro-fiber with a diameter of 6.6μm.