Raman spectra of as-prepared porous silicon are obtained using 457.5 nm solid-state laser from which some relations between peak parameters and laser powers are also got. The experimental phenomena of the Raman peaks near 520 cm-1 and 300 cm-1 are extensively explained. The red-shift and asymmetrically broadening of the Raman peaks near 520 cm-1 and 300 cm-1, which are reversible with the increase and decrease of the laser powers, are thought to be derived from quantum confinement effect (QCE) when the mean particle size shrinks as local temperature increases, and this obeys the basic rule of thermodynamics. The apperarance of double peaks near 520 cm-1 at high powers are thought to be the cleavage of longitudinal optical (LO) and transverse optical (TO) modes when the mean particle size reaches a certain threshold.