Abstarct: Power flow is one of the major issues in the steady state system analysis which is used for planning operations and evaluation of the performance of a power system. In the presence of distributed generation (DG) sources and with respect to the characteristics of a distribution network, it is not feasible to use conventional power flow methods. Hence, it is necessary to find an effective method with simple and accurate calculation is sensible. Generally, of the loads considered to be constant power. However, some of them are voltage dependent load that are approximated by exponential functions and polynomials. Moreover, existence of unbalanced loads, makes the system to be unbalanced. The imbalance increases with load increasing. In this thesis, the backward-forward approach is used as one of the most widespread methods with low computational complexity and proper accuracy in flow analysis of distribution systems. The proposed approach consists of two main steps. In the first step (the backward step), current calculations is started from the end of the system to the reference point and. In the second step (the forward step) the voltage calculations is started from the reference point to the end of the system. The approaches repeated until the suitable convergence is attained. In the power flow computations the required components in flow analysis of distribution systems will be modeled. In the equations of the power flow the load models and unbalanced loads as well as DG sources are considered. The proposed algorithm is implemented on three standard test systems and all simulations are performed in MATLAB. The simulation results show that the proposed algorithm is fully capable to perform power flow considering load models, unbalanced loads and DG resources.