The traditional cathode electrophoresis kinetic equation was revised, combined with the analysis and theoretical studies of the characteristics of magnesium alloy. A revised kinetic equation (3 . 6 X10¹¹δ²+4 . 77 X10⁵δ = t) of a typical magnesium alloy AZ31 was obtained by the experimental verification for their rationality and validity, which provided a theoretical guidance for the preparation of electrodeposited coating on magnesium alloy.