The theoretical and experimental results about the surface electron subband structure in N-type inversion layer for the P-type Hg_(1-x)Cd_xTe MIS structure samples have been disoussed. The model and the related method to investigate quantitatively the surface electron subband structure by using the capacitance-voltage spectroscopy, cyclotron resonance spectroscopy and magneto-conductivity oscillations have been desoribed. Starting from the Kane model and taking into account the surface electron spin-orbit interaction, the subband dispersion relation, Landau level and effective g~* factor have been obtained, which agree well with the subband electron cyclotron resonance and spin resonance results measured for the P-type Hg_(1-x)Cd_xTe samples. Based on these results, the zero field spin splitting effect, the shifting and crossing effect of Landau levels as well as the wave-function mixture, etc., arising from the surface electron spin-orbit interaction have been investigated quantitatively.