The equations describing the density variation of the ion and the electron in the inhomogeneous and collisional plasma are obtained. The dispersion relations are obtained and the mode coupling equations between the waves satisfying the dispersion relation are derived. The mode couplings are associated with the drift waves with long wave length ($k_{\bot} \rho_i \ll 1$) and the 3 dimensional convective modes defined in this thesis. From the mode couplings, a nonlinear mechanism for the excitation of the 3 dimensional convective mode through the decay of a monochromatic drift wave is analyzed. Further analysis is also given for the generation of the convective modes by the long wavelength drift wave. A qualitative analysis is also made of the shear stabilization effect.