The effect of positron irradiation on photoluminescence（PL） of porous silicon has been studied. After four hour positron irradiation

the red PL spectrum of porous silicon blueshifts into greenish spectral region

and a higher energy luminescence band is introduced into this blueshifted spectrum The fourier transform infrared absorption experiment shows that the positron irradiation can cause further oxidization of porous silicon. A possible mechanism causing this change of PL spectra after positron irradiation is suggested.