The side-hole package technology, a novel fiber grating pressure sensitivity enhancing scheme, is presented. The pressure sensitivity is improved several orders using side-hole package technology, which has reduced the dependence of pressure sensitivity on polymer material parameters through changing package structure. The pressure-sensing model of side-hole package is built using the finite element method and the influence of package geometric configuration on pressure sensitivity is analyzed. The experimentally measured results show that the pressure sensitivity of fiber grating with side-hole package is 5251 pm/MPa, which is 1750 times that of without package. The cross-sensing problem is suppressed by three orders and the sensor can satisfy underwater pressure measurement with high accuracy.