Seawater electrolysis is a sustainable technology for producing hydrogen that would neither cause global freshwater shortages nor create carbon emissions. However, this technology is severely hampered by the insufficient stability and the competition from the chlorine evolution reaction (ClER) in actual application. Herein, a metal–organic framework (MOF)‐on‐MOF heterojunction (Ni‐BDC/NH2‐MIL‐88B(Fe)) denoted as (Ni‐BDC/NM88B(Fe)) is synthesized as an effective oxygen evolution reaction (OER) electrocatalyst for high‐performance seawater electrolysis, which exhibits a long stability of 200 h and low overpotentials of 232 and 299 mV at 100 mA cm−2 in alkaline freshwater and seawater solution, respectively. The exceptional performance is attributed to the rapid self‐reconstruction of Ni‐BDC/NM88B(Fe) to produce NiFeOOH protective layer, thereby avoiding ClER‐induced dissolution. Moreover, the interface interaction between Ni‐BDC and NM88B(Fe) could form the Ni─O─Fe bonds in Ni‐BDC/NM88B(Fe) to promote the electron transfer and lower the energy barrier of the rate‐determining step, thereby accelerating the OER. These electrochemical properties make it intriguing candidate as an efficient electrocatalyst for practical alkaline seawater electrolysis. A hetero‐structured Ni‐BDC/NM88B(Fe) metal–organic framework is synthesized to be as an outstanding electrocatalyst for seawater oxidation. The unique electronic channel (Ni─O─Fe) in this heterostructure not only enables the rapid reconstruction to generate the protective layer of NiFeOOH, thereby avoiding the effects of CER, but also optimizes the adsorption energy of the intermediates, leading to superior seawater oxidation performance.