AC arc generated during the electromagnetic relay (EMR) action process under AC load will cause the contact erosion and shorten the life time of relay.The increasing of contact gap is favorable for extinguishment of the AC arc, but it will also result in the increasing of magnetic gap, which may further influence the electromagnetic force and the dynamic features of the relay.In this paper, a certain type of AC loaded EMR is studied.Firstly, the relationship between contact gap and AC arc duration is analyzed, which can provide the theoretical basis for the optimization of contact gap.Then, limiting conditions of optimizing the relay contact gap is determined by real arc experiment of different contact gap, and considering such limiting factors as actual product dimension and processing process, finally obtains the optimization solution.In the end, the optimization results for the relay are verified by the real product complete-period life test.