For quickening the gas sensing speed of fiber Raman detection system, a fiber Raman analyzer with sideopened configuration is proposed and explored. For exploring the relationship between Raman intensity and fiber parameters, a Raman sensing model is introduced for optimizing effective mode area and enhancing normalized intensity overlap between Raman sensing light and analyte. Calculations predict that there is a trade-off between Raman intensity and fiber parameters, while the optimal trade-off dependes on the refractive index of the background material, core diameter and strut′s thickness. The optimized fiber core size for silica-based fiber Raman analyzer is 120~150 nm.