In order to effectively solve the problems of large size, high signal loss and poor switching efficiency of microwave test instruments such as signal or spectrum analyzer, RF MEMS switches were applied to optimize the structure of MEMS interdigital switchable filter. The interdigital resonators with different center frequencies were selected through MEMS four-throw switches to realize the switching of four frequencies in the range of 6 to 14 GHz. The insertion loss of the four switchable frequencies obtained by optimizing calculation which used to calculate the geomemtric parameters of the filtering structure through HFSS were 1.26 dB @6.86 GHz, 1.03 dB @9.16 GHz, 1.23 dB @11.78 GHz and 1.07 dB @12.26 GHz respectively. The overall area was about 7.95 mm3. Compared with other switchable filters, this filter integrated MEMS four-throw switches with interdigital resonators, and had the advantages of low insertion loss, small size, and high integration.