We investigate in detail the influence of second-order ionization processes on the photo-electron spectrum etc., which has been ignored previously in the study of intense laser-field induced autoionization. It is found that, in the region of laser intensity currently discussed in literature, many physical features are altered significantly. (1) Under certain conditions, line-narrowing effect disappears. (2) The olignal photoelectron peaks are greatly reduced. (3) In agreement with the most recent experimental findings on multiphoton ionization, high-order photoelectron peaks drastically increase with increasing laser intensity, and they dominate the original peaks for sufficiently high Intensities.