To elucidate the promotion action of cobalt on Mo sulfide catalysts, UPS, XPS and LEED have been applied to study the submonolayer deposite process of promotor metal Co on the active catalytic phase for Co-Mo catalyst-the highly edged surfaces and ion sputtered basal plane of MoS2 crystal. At a certain submonolayer coverage of deposited Co, the new Co-correlated interface states could raise surface EF to a new higher pinning position by about 0.30-0.35eV. So the surface barrier and work function for these catalytic active phases are decreased. The remarkable changes for electronic structure near EF and the studies of LEED patterns reveal that the active phase Co-Mo-S, in which the Co-Mo bond appears to behave in much the same way as in the intermetallic bond, could be formed by locating the promotor Co at the surface disorder defects in edge sites.