To solve the problems of poor out-of-band suppression ability and uneven in-band group delay of RF MEMS filters, an L-band RF MEMS linear phase filter with narrow bandwidth, low insertion loss and high selectivity was designed. Narrow-band transmission was realized by selecting substrate material with high dielectric constant, and linear phase was realized by using resonator with double-layer inter-digital structure. The volume of the circuit was reduced. The HFSS software was used to optimize the performance of the filter. The results showed that the center frequency of the filter was 1.46 GHz, the in-band insertion loss was less than 1.97 dB, the in-band group delay fluctuation was less than 2 ns, and the out-of-band rejection was more than 70 dB at 1 GHz around the center frequency. The overall circuit size was 10 mm×7.2 mm×0.62 mm.