The catalytic properties of a series of (dppe) MCl2 [M = Fe(II), Co(II), Ni(II)] in combination with EAO (ethylaluminoxane) for ethylene oligomerization have been investigated. Treatment of the bidentate phosphine metal complexes with EAO in toluene generated in situ active catalysts which catalyze oligomerizaton of ethylene to low-carbon olefins. The effects of reaction temperature, ratios of n(Al) : n(M) and reaction periods on catalytic activity and product distribution have been studied. The activity of cobalt complex with EAO at 200C was 4021 g/g(Co)h, and the selectivity of C4-10 olefins is 95.5%. The catalytic properties of a series of (dppe) MCl2 [M = Fe (II), Co (II), Ni (II)] in combination with EAO (ethylaluminoxane) for ethylene oligomerization have been investigated. Treatment of the bidentate phosphine metal complexes with EAO in toluene generated in situ active catalysts which catalyze oligomerizaton of ethylene to low-carbon olefins. The effects of reaction temperature, ratios of n (Al): n (M) and reaction periods on catalytic activity and product distribution have been studied. The activity of cobalt complex with EAO at 200C was 4021 g / g (Co) h, and the selectivity of C4-10 olefins was 95.5%.