In this thesis, we construct a mathematical model for Sectorized FFR Networks (SFN). In SFN, frequency allocation adopts FFR (Fractional Frequency Reuse), which divides the frequency into two parts: the super group (Sup-G) and the regular group (Reg-G). Since the frequency allocations of Sup-G and sectors overlaps each other, and the same frequency band is used by two Sup-G in two different BS, when the radius of Sup-G is too large, interferences will occur among the adjacent BS. In our mathematical model, given different environmental parameters (number of sector, number of MS, strength of power), we can compute the system capacity by varying the radius of Sup-G and the various environmental parameters. In practical applications, since the number of MS becomes smaller in the cellular edge and it increases rapidly in the cellular center, Gaussian distribution is more adequate to model the distribution of MS. Thus, in the calculation of interference, we take the integration of the path loss multiplied by the transmission power and the MS density. Finally, through the SINR and Shannon Capacity formula, we can derive the overall system capacity. From the mathematical model, we can achieve a ratio of Sup-G radius and cellular radius. With this radius ratio, an MS can have about the same capacity regardless of the position in the FFR network. Otherwise, an MS may get very different capacity when it moves to the cellular edge or sometimes it appears in the cellular center. Additionally, from the mathematical model, we can analyze the interferences and system capacity for different numbers of sectors.