The effect of varied H+ concentration on surface morphology of porous silicon (PS) is observed by atomic force microscopy technique. A new mechanism of PS formation concerning H+ effect is proposed. The photoluminescence (PL) spectra of two typical PS samples have different responses in the short-wavelength region. Surface photovoltage spectra results imply that the short-wavelength PL band of the PS sample prepared in high H+ concentration may be related to direct band-gap transition.