A compact plasmonic coupled-resonator system, consisting of a stub resonator and baffles in the metal-insulator-metal waveguide, is numerically investigated with the finite element method. Simulations show that sharp and asymmetric response line-shapes can occur in the system. The asymmetric line-shapes in the transmission spectra depend on the relative positions of the resonant wavelengths between the single-stub resonator and the inner resonator constructed by the baffle and the stub resonator, while the other part of the transmission spectra (except the asymmetric part) maintains the spectral features of the structure constructed by the baffles. An analytic model and a relative phase analysis based on the scattering matrix theory are used to describe and explain this phenomenon. These sharp and asymmetric response line-shapes are important for improving the nano-plasmonic devices' performances.