Abstract: In this paper, a 2-layer nonlinear primitive equations model is developed and evolved at low spectra for the solution of nonlinear equation groups. The evolution of the solutions and their corresponding circulation are discussed with changing external parameters and they are compared with linear response. In addition, the stability of constant solution is studied.Main conclusions: (1) A more realistic mean zonal equatorial circulation is forced by components of the diabatic heating in the non-linear response. (2) In this response, warming by latent heat exerts a dominant effect on zonal circulation. Abrupt changes in the solutions can occur with the variation of external parameters. Their corresponding zonal circulation changes from one constant state to another, in which latent heat from convection plays a dominant role, followed by warming by sensible heat. (3) The effects of radiation heating on circulation differ for nonlinear and linear responses; warming by latent heat has similar effects on circulation, though much stronger for nonlinear response.