Abstract: In a buffer solution of trihydroxyethylamine (TEA,pH 7.6),a sensitive reductive polarographic wave was found by single-scanning oscillopoldiography with its peak potential at -1.07 V (vs.SCE),given by Co2+ ion due to the formation of a mixed coordination complex of Co2+·(DMGX)2·(NO-2)2.Linear relationship between the peak potential and the cobalt(Ⅱ) concentration was found between the range of 2.2×10-9-6.6×10-6mol·L-1 (r=0.999 7) with a detection limit of 7.4×10-10mol·L-1.The mechanism of the electrode reaction was studied and the polarographic wave was proved to be an adsorption-catalytic wave given by the tri-componental complex as mentioned above.