Nowadays active power filter (APF) is well known technique for improving the power quality .It mitigates the level of harmonics to acceptable ratio, also it overcomes voltage sag and improves power factor. There are different types of APF according to its application. This paper will introduce a detailed design of a Shunt Active Power filter (SAPF). Firstly trial and error method will be used to select acceptable value for conventional filter PI controller parameters, Secondly particle swarm optimization (PSO) technique is used for tuning the filter PI controller by optimizing the optimal controller gains. The presented design is modeled and simulated by using MATLAB-SIMULINK toolbox. Many contributions such as design and simulation of SAPF, besides practical modeling of a nonlinear load for studying the effect of SAPF on the integrated system.         A practical verification is done and compared to the proposed simulated system. It is found that a good agreement between the experimental result and the modeled one. A costless   method based on Virtual experimental technique is also used and applied to large scale systems for obtaining predesign system with acceptable accuracy. The proposed filter can be adapted for any other loads with acceptable total harmonic distortion (THD) under the norms of IEEE (519-1992).