In this paper, the polarographic catalytic wave of trace chromium in seawater and its mechanism are studied.In supporting electrolyte containing ethylene diamine-NaNO2-EDTA, a clear, sensitive and stable catalytic wave is obtained, and its largest peak potential in differential oscilloscopic pola-rogram is -1.7V (S.C.E).The detection limit for Cr is 1.5×10-9 M.It is unnecessary for natural seawater samples to be separated and preconcentrated, and the samples can be directly detected.Variable coefficient is 5%, and the relative error of recovery efficiency, 10%.The wave is a kind of hydrogen catalytic one with absorbability.