Abstract: Marine ranching required self-sufficient electrical power because they were often built near coastal areas that were not accessible to the grid. Distributed power generation offered flexibility, reliability, and efficiency for this application. This research aimed to propose a power-quality management system that detects harmonics using i_p-i_q method based on the instantaneous reactive power theory, and then suppressing those harmonics using parallel active power filtering（APF）. Simulation experiments in MATLAB showed that the i_p-i_q method detected harmonics more rapidly than traditional Fourier analysis. If the voltage waveform was distorted or the load was nonlinear, the harmonics were detected more consistently than p-q method. APF could generate opposite phase compensating current in real time that effectively suppress the harmonics detected by the i_p-i_q method. The test results showed that harmonic detection and suppression based on i_p-i_q method and APF reduced the total harmonic distortion（THD） from 16.77% to 4.44%. This research provided a new idea for harmonic detection and suppression in marine ranching distributed generation power quality.