The influence of the different gas ratios (SO2/Ar) on the vibronically resolved laser-induced fluorescence excitation spectra of the SO2( 1A2— 1A1) system was investigated under the supersonic jet conditions.High resolution spectra of two complete progressions (1,m,1),(0,n,1) were obtained,in which the rotational structures of the (0,9,1),(0,10,1),(1,7,1),(1,5,1)-(0,0,0) bands were observed,for the first time,so long as we know.The assignments of 847 rotationally resolved lines were based on an asymmetric top simulation,which results in the determination of the rotational and centrifugal distortion constants of each vibrational level of state.The approximate geometry parameters of state was derived to be r(S—O)=0.160nm,∠OSO=101.64°.In addition,a discussion on the inertial defect of each vibrational level of state was presented.