Abstract: Donnell theory and FEA (finite element analysis) software is employed to analyze the strength and stability of GRP towing body of a buoy system. First, by adopting Donnell cylindrical shell equation and constitutive relations of laminated plate, a stability calculatig method of simple supported thin orthotropic shell under hydrostatic pressure, is obtained. With the equation, we can analyze the buckling strength of the main part of the towing body. ANSYS tool is then used, to calculate the strength and stability of the structure. In consideration of the strength, stability and weight of the body, we changed the parameters with different values with respect to material ply, thickness of the shell and size of the ribs for a rational structural design.