A new input interface circuit with single event effect hardened is proposed, which adopts the scheme of combinational logic operating after delay-processing. This circuit is designed and implemented in 0.8 μm 600 V Bipolar-CMOS-DMOS(BCD) process of Communication Mode Selector Control(CMSC). The single event radiation experiment has been completed in National Space Science Center. The results of simulation and test show that the circuit proposed in this paper can effectively immune to Single Event Upset(SEU) whose Linear Energy Transfer(LET) is under 80 MeV·cm2/mg. Especially for the case that multiple nodes occurring upset at the same time, the proposed circuit has high capacity of SEU–tolerant.