In comparison with mononuclear metal catalysts in olefin polymerization, bimetallic catalysts having two active species significantly affect catalytic activities and properties of resulting polyolefins(such as microstructure of polymer, molecular weight and polydispersity). Herein we highlight the recent progress of bimetallic catalysts in ethylene polymerization and co-polymerization, which have been illustrated through the differences of metals used either early transition metals(Zr, Ti, Hf) or late transition metals(Ni, Fe, Co), and the varieties of ligands including constrained-geometry catalyst(CGC), phenoxyimines, azaallyl, a-diimines as well as iminopyridines. On the basis of these results, the early-transition metal catalysts have achieved not only homo-polymerization of ethylene but also co-polymerization of ethylene with α-olefin, while the late transition metal catalysts catalyze efficiently polymerization of ethylene, resulting in highly linear polyethylene by iron and cobalt catalysts or higher branched polyethylenes by nickel catalysts.