The design of the radio frequency attenuator was based on the MEMS switch. First of all, the basic structure of the electronic circuit was presented with CPW as the transmission line, the contact MEMS switch as the controller and the electric capacity in the switch as the balance criteria to match the Q value. Secondly, the size of cross section of waveguide was calculated abstractly. Thirdly, the resistance values in the T system were calculated according to the reduction. From the simulation on the CST microwave studio, the comparison of S values of first-order and second-order attenuator revealed that the radio frequency could keep a stable reduction in the wider band after the Q values were matched. Finally, the attenuator was sampled and tested. The result shows that the work frequency range of attenuator could be extended by Q value match which is a new feasibility for the stable attenuation of high frequency signal.