The propagation characteristics of rectangular waveguide filled with two layers of single-negative medium are analyzed in this paper. The Drude-FDTD model is adapted to the application in three-dimension simulation program. Simulation results show that a subwavelength transmission mode exists in the waveguide. Based on the simulation results for different frequency and different medium parameter, energy propagation rule in this kind of waveguide is obtained. Especialy, the band width of microwave devices and antennas can be significantly widened with ENG-MNG filling method.