In this paper the experimental results of laser multiphoton ionization of background gases (mostly oil-vapor) in the vacuum chamber for laser produced plasma study are presented by using high power laser irradiation. According to the time-of-Sight-spectrnm of the ions with different specific charge, the obtained ions can be divided into four groups: H+, H2+; C+, CH+, CH2+, CH3+ N+, O+; C2+, C2H+, C2H2+, C2H3+,C2H4+, Si+, CHO+, O2+ and C3+, C3H+, C3H2+, C3H3+. Moreover; C++ ions have also bssn obseved. Finally by adding argon gas with definite concentration into the vacuum chamber, Ar+ is observed.