A three-dimensional diagnostic model has been developed to compute the monthly mean circulation and sea surface topography in the Western Tropical Indian Ocean north of 20 degrees S and west of 80 degrees E. The diagnostic model equations are the basic ocean hydrodynamic equations of momentum, hydrostatics, continuity and sea surface topography. There are total five equations in five unknowns. While the hydrodynamic equations of momentum, hydrostatics and continuity are solved by a leap-frog numerical scheme, the sea surface topography equation is solved by successive over-relaxation technique. Model has 18 levels in the vertical with a maximum depth of 900 meters, a resolution of 1 degrees in the latitute and longitude directions and is forced by climatologically averaged monthly mean winds temperature and salinity data (density anomaly). Model computed resulted of sea surface topography for all the 12 months and its associated circulation are analysed and presented in this paper.