Bi- substituted garnet films are most promsing of the next generation of themagneto-optical recording medium. In this paper we present the construction of a newoptimization objective function, which combines readout and thermal writing in a magnetooptical recording process. The method proposed is succeeded in the optimization design ofmagneto-optical disks, the structure of which is Bi-substituted DyGaIG/metal reflectivelayer (Al)/Glass. The result shows that the new optimization objective function would have more realistic significance.