An optimization of the frequency spacing factor, S factor, of a pseudo orthogonal frequency coding (POFC) system has been studied with the consideration of the crosscorrelation of the adjacent center frequency of chips and the utilization ratio of spectrum. The fundamental principles of orthogonal frequency coding (OFC) and POFC are introduced. The COM model of POFC is analyzed and the cross-correlation of adjacent center frequencies of a POFC system is derived. The peaks of crosscorrelation are extracted by the computation. The relationship of S factors and peaks are found at last by the analysis of scatter diagram and fitted curve. The reasonable interval for S factor of this POFC system can be obtained from the analysis of peaks with the region of [1.49, 1.83], [2.1, 2.63] and [3.12, 3.415]. All of the studies are proved by the analysis of the extracted signals of a COM model. It will also guide the design of the POFC systems.