Power flow analysis plays a significant role in both design and operational stage. The purpose of any load flow analysis is to compute accurate steady state voltages and voltage angles of all buses in a network, the real and reactive power flows into every line and transformer, under the assumption of known generation and load. This paper focus on fast decoupled flow, a practical power system has been used as an example to introduce its application in actual calculation, what’s more, develops a fast decoupled load flow calculation program for n-node system by taking advantage of MATLAB. A visual GUI interface is also established with MATLAB. In addition, the paper proposes a new simple power system data format, different from the IEEE standard one. The correctness and simplicity of the proposed format is verified through IEEE-5bus,-9bus,-11bus,-39bus systems.