There are two peaks of different polarizations in the reflection spectrum of the side-hole fiber grating and their separation interval has a linear variation along with the pressure changing while it is insensitive to the temperature. We have proposed a novel measurement scheme based on polarization detection. The detection of peak separation is achieved by measuring the two peaks center wavelengths separately with all polarization maintaining fiber system. The side-hole fiber grating pressure sensing within, the range of 0∼3.5 MPa is realized successfully with the new scheme.