In this paper, three phase sequence decouplingcompensation models of unsymmetrical transmission lines are introduced first. By combining these models with the wellknown Newton-Raphson and Fast-Decoupled algorithms, two novel methods - Sequence Decoupling-Compensation NewtonRaphson (SDCNR) and Sequence Decoupling-Compensation Fast-Decoupled (SDCFD) Methods used for three phase load flow study are proposed, which can be used to analyze both normal and abnormal three phase power system steady state operation. The computation accuracy, computation speed and convergence characteristics of these methods are then investigated. From these investigations, their advantages of high accuracy, high speed, reliable convergence are verified. In this paper, parallel implementation of these methods is also discussed.