In mobile networks, such as fifth generation (5G), the appealing characteristics of the small cells, like easy deployment, affordable, and low power usage, have led to improvement of Heterogeneous Network (HetNet) technique. In HetNet, the restricted resources are usually shared by the small cells, that in turns results in an interference issue challenges. The latter may be regarded as the main barrier for appropriate HetNet performance. In this paper, both Inter Cell Interference and Intra Cell Interference are studied and evaluated for Al-Najaf governorate 5G network. The network performance was investigated before and after interference mitigation. The simulation results are dependent to evaluate the effectiveness of all approaches and schemes that are implemented to cope with both inter and intra cell interference. The simulation of the network is performed by the aid of Integrated Communications System (ICS) telecom software. In Inter-Cell Interference, in term of modulation, it obviously shows that higher modulation occupies only small portion of the covered area due to interference. The modulation scheme 64 Quadrature Amplitude Modulation (QAM) 3/4 occupies 13% from the total covered area with omni profile, while this scheme is being missed with 4-sectors profile due to interference. Intra-cell interference is materialized as Inter Carrier Interference( ICI) and Inter Symbol Interference(ISI), the effect of Cyclic Prefix( CP) on the network performance in terms of ICI is tested based on the simulation of the 3D reflection paths; for the adopted test area, the interfered area equals to 27.06% km2 according to 5.7μsec guard interval, while the interfered area is reduced to 6.42% km2 according to 11.4μsec guard interval. The interfered area is reduced by 21% due to ICI when the CP is extended from 5.7µsec to 11.4µsec. CP adopted in this work equals to (1/8), which is the mostly used.