In the present paper, we used the data of g-factor value, linewidth Hpp, and spin density Ns from ESR measurement to investigate the defects in SIPOS film. There are four defects related to the different Si tetrahedral structures Si - (Si4 - YOY) in SIPOS film. These defects are named defect 1, defect 2, defect 3, and defect 4. The ESR spectrum found for a specific oxygen content is assumed to be a linear superposition of the resonance of these four defects. The g-value is the statistical average of four g-values' corresponding defects. Using the above model of defects, the variations of linewidth and spin densities of SIPOS film with different oxygen content and annealing conditions can be well described.