The present study was made to obtain useful information for design of cobalt-based alloys with good high temperature strength properties by using the DV-X_α cluster method. The tendency of the local spin moment curve obtained from the present calculation was shown good agreement with the Slater-Pauling curve. The changes in the bond orders with alloying elements could be understood from the electron density difference maps. Using two calculated alloying parameters, the bond order(Bo) and the d-orbital energy level(Md) of transition alloying elements, the binary phase diagrams of the Co-M system could be classified according to the location in the Bo-Md map. These results will give some guide to design of cobalt-based alloys for high temperature applications.