The extensive and ever increasing application of nonlinear loads have introduced power quality problem in distribution system. The nonlinear relation between voltage and current may cause harmonic currents that propagate through the distribution network causing voltage distortion. The presence of higher frequency components in the distorted voltage may lead to a possible dangerous resonance and significant voltage increment that can be destructive. The higher frequency components of the voltage may be suppressed using filter and the distortion may then be mitigated. For the purpose of analyzing the system including nonlinear loads and the related voltage distortions, a harmonic power flow calculation is developed. A relatively fast and accurate approach for harmonic analyses using decoupled technique is proposed. The system with a number of harmonic generating devices may be analyzed and a number of passive filters are then installed to alleviate the distortion assuring the compliant to the IEEE 519 Standard. The size and location of the filters are tentatively determined and the system improvement is observed. The effectiveness of the proposed strategy is implemented on a 123-bus IEEE distribution system including a number of nonlinear loads. The capability of the decouple approach accepting measurement results may lead to real implementation.