As the global demand for potassium continues to increase, the potassium in natural resources is gradually insufficient. The potassium resources in the ocean are extremely rich. In this paper, a new battery deionization method (BDI) was developed to selectively recover potassium from seawater using a Fe[Fe(CN)6] (BG) battery electrode. The BG-based electrode exhibited totally different insertion behavior to the most abundant cations in seawater, with the capacity order of K+>Na+>Li+>Ca2+>Mg2+. Using the battery cell assembled with BG and activated carbon electrode, the recovery capacity of K+ arrived at 177 μmoL/g under the discharge stage of battery from 0.8 to 0 V, and no significant variation was found even in the presence of 37 times higher concentration of Na+ than that of K+. In synthetic seawater, the BG battery electrode still kept the recovery of 69.6% for K+ with the separation factor α(K+/Na+) of 141.7. Moreover, energy consumption is calculated to be 15.4 kJ/mol, 10 times lower than that of the capacitive deionization method. Meanwhile, the BG battery electrode is very stable with the adsorption amount retaining 86% over 150 cycles. The three-cell stack test in synthetic seawater proves that the current BDI device is easy to be amplified for recovering potassium from seawater.