We report the photoluminescence of monocrystalline silicon irradiated by femtosecond pulsed laser in different environments (deionized water and air) and energy density conditions. The field emission scanning electron microscope (FESEM) measurement results show the formation of completely different morphologies on silicon surface in different environments. A stripe-like microstructure on the silicon surface in air is formed in contrast to the smaller and coral-like microstructure generated in the deionized water. By using the energy dispersive spectroscopy (EDS) we find that silicon and oxygen is the main elemental composition on femtosecond laser-induced silicon surface, and the content of oxygen on the sample surface formed in the deionized water is nearly four times larger than that in air. The Si-Si bond (610 cm-1) and Si-O-Si bond vibrations (1105 cm-1) are detected mainly in the Fourier transform infrared transmission spectrum (FT-IR). The photoluminescence (PL) spectroscopy measurement results show that visible blue luminescence is observed both from the silicon ablated in the deionized water and in air, while the shape and position of the emitted luminescence peak are substantially the same. However, the luminescence intensity of silicon etched in the deionized water is close to 3 times stronger than that in air when the photoluminescence is excited at respective most suitable excitation wavelength. A more interesting phenomenon is that the position and shape of the photoluminescence peak in the visible range are basically not changed. The studies confirm that oxygen plays an important role in photoluminescence enhancement. Photoluminescence may be mainly generated by the formation of oxygen defects SiOx and the content of low oxide SiOx (x<2) determines the luminous intensity level.