Mathematical model for co-current spray dryer is developed . The model is axisymmetric dimensional model and two way coupling .It includes the mass, momentum, and heat transfer for a single drying droplet as well as for drying medium . The system used is water-air. The model used a system of equations to compute the axial and radial distribution of droplet diameter, its velocity , temperature and rate of evaporation , and air temperature , humidity and velocity in spray drying chamber . The model includes a system of non linear first order differential equations as a function of the axial distance of the spray drying chamber . The results obtained from the model are shown to be in agreement with experimental results.