The internal defects are induced by irradiating pure silica glass with different hydroxyl concentrations by femtosecond laser pulses. Influences of hydroxyl concentration, laser pulse width and laser power on the type and concentration of defects are systematically investigated. The micro fluorescence spectra, absorption and emission spectra of silica glass show that the tested samples produce three kinds of defects including non-bridging oxygen hole center (NBOHC), non-relaxation oxygen deficient center [ODC(Ⅱ)]and E′ center. ODC(Ⅱ) defect is easier to be induced when the hydroxyl concentration is lower, while NBOHC defect is easier to be induced when the hydroxyl concentration is higher. The obvious red fluorescence (650 nm) under ultraviolet lamp excitation (254 nm) in irradiated glass with high OH content can be observed. It is found that red fluorescence (650 nm) intensity closely depends on the laser pulse width and laser power, to be specific, it increases at first and then decreases with the increase of laser pulse width, and increases at first and then tends to slow with the increase of laser power.