A kind of surface plasmonic waveguide with double parallel columniform metallic nanorods coated with the gain medium is introduced. The dependence of distribution of longitudinal energy flux density, effective index, propagation length and mode area of the fundamental mode with longer propagation length supported by this waveguide on geometrical parameters and electromagnetic parameters are analyzed using the finite-difference frequency-domain (FDFD) method. Results show that the longitudinal energy flux density distributes mainly in the middle area which is formed by the two columniform metallic rods. The propagation properties can be adjusted by changing the geometrical parameters and electromagnetic parameters. The propagation length can be extended obviously with the help of the gain medium. This kind of surface plasmonic waveguide can be applied in the field of photonic device integration and sensors.