Abstract: The analysis on aperture scattering is an important composition of electromagnetic protection research on complex electronic system. A mathematic model of aperture scattering was built on the base of two-port network theory and electromagnetic topology theory, with which a generalized scatter matrix was designed. A data sieving strategy was formulized for least square support vector machine, based on which a new algorithm for aperture scattering matrix with evolving ability was proposed. By use of the simulation data of an rectangle aperture cavity s HFSS model, the aperture scattering model was tested. The mean absolute error of the forecasting about reflection and transmission are ±1.2 mV/m and ±3.3 mV/m, while the mean relative error are ±0.17% and ±8.29%. At the precision of 90%, the absolute error of forecasting about reflection and transmission are less than and, while the relative error are less than ±0.39% and ±0.93%, which means the aperture scattering is predicted accurately. The practicability and reliability of the method are proved.