The configuration of Tandem Cylinders is a typical one in researching noise and interactions between different components, where the Distance-diameter ratio is a very significant parameter with which the flow form varies a lot. To clearly research the ratio’s effect on Tandem Cylinders flow as well as the unsteady flow physics, a reduced-order model is built where Proper orthogonal Decomposition(POD) is used to extract reduced basis modes, and Kriging model is used to train sample data and interpolate projection coefficents for each reduced basis. To ensure the snapshots’ accuracy, the scale-adaptive simulation (SAS) model based on k-SST turbulence model is used to predict time-dependent flow field. By comparing with solutions provided by the numerical solver as well as experimental data, the reduced model presents a good accuracy and efficiency. And then based on the reduced basis, the change regulation of the time-average flow is summarized.