Coupling of surface plasmon (SP) waves between two metal-dielectric interfaces of a dielectric-metal-dielectric (DMD) waveguide, in which one of the dielectric layers is incorporated with optical gain, is proposed to realize plasmonic lasing. The propagation characteristics of the SP waves supported inside the DMD waveguides are studied by finite-difference time-domain method. It is found that there are optimized thicknesses for the metal film and gain region to obtain minimum propagation loss. Furthermore, a coupled-mode model is developed to analyze the lasing characteristics of the DMD waveguides with coherent optical feedback. The conditions to achieve single-longitudinal-mode lasing from the DMD waveguides are also investigated.