Atomic force microscopy (AFM) has been used to study the pore wall structure of p-type macroporous silicon. Nanometer size particles are found to distribute on the pore wall of the luminescence macroporous silicon samples. Combided with the analysis of photoluminescence (PL) spectra, it can be concluded that the PL phenomenon of macroporous silicon should be due to the quantum confinement in these nanoparticles distribution on the pore wall.