Separating the load impedance of the resonant frequency selective surface (FSS) can form the complementary frequency selective surface (CFSS), whose filtering feature is based on the coupling mechanism. The resonance of CFSS can be tuned by controlling the rotation angle of the element on the capacitive surface. Taking tripole element for example, the frequency response of the CFSS is calculated by using the coupled integral equation method. A 250 mm250 mm prototype is tested via free space method. Calculation and test results show that the resonance of the CFSS can be tuned actively as the rotation angle changes. This study provides reference to the active FSS design.