Abstract: The traditional diagnosis and tuning method for microwave filter only extract, the equivalent circuit parameters, but not the tuning magnitude. The couplings between the tuning elements are not considered, and it is very inefficient. In order to diagnos and tune the microwave filter quickly, we must determine the tuning direction and value. An improved tuning method based on genetic algorithm and aggressive space mapping is presented in this paper. The measured or simulated parameters such as S parameters are not suitable for parameter extraction directly. The phase shift effect must be removed before parameter extraction. The phase shift effect is moved by using the genetic algorithm. The equivalent circuit parameters are extracted through Cauchy method after the phase shift effect is removed. The tuning direction and value are determined by aggressive space mapping, which makes the filter meet the specifications. A fourth order cross-coupled filter tuning example is used to verify the new method and shows the validity of the method. The filter meets specifications less than four iterations. The method presented in this paper can be applied to other type filter diagnosis and tuning.