Power quality problems in the distribution system can sometimes lead to unbalanced and uncontrolled conditions during operation. This situation can be overcome by estimating the parameters of the distribution system, thus solving the problem of load distribution. The presence of harmonic loads in the distribution system complicates the operation of the system and requires new algorithms to obtain a specific solution rather than an approximate solution. Taking all these aspects into account, this paper presents a new methodology based on decoupling by formulating intrinsic and mutual impedance networks and mathematical modeling of these networks along with ancillary methodology. This methodology is applied to solve an unbalanced distribution system with 13 nodes and 11 harmonic loads connected in different parts of the system. The obtained results are confirmed by the existing literature methods.