A Quadrilayer with PtCo alloy as a MO layer was suecessfully prepared. Based on the quadrilayer,the effect of the thickness of each layer upon Keer rotation, reflectivity and figure of merit was studied and an optimum optical structure was shown. For the thermal design, an optimum structure suitable for thermo-magnetic recording was obtained.When considering the effect of the reflectivity, the Keer rotation can be enhenced by decreasing the reflectivity. Therefore, the structure design shoud be carried out by considering reflectivity, Keer rotation and temperature of the MO layer at the same time.An optimum thermal and optical structure was given.