In order to obtain an accurate and feasible explosive reactive armor(ERA) detonation calculating method of pre-warhead jet after penetrating seeker., First the processes of jet formation and passinginterference through the equivalent interference of seeker arewas calculated by the using ALE method.Afterward, a SPH model reconstruction method was proposed, and the head jet after penetrating seeker interference was transformed into a three-dimensional SPH calculation model.Using the SPH model, a studyresearch of the front warhead penetrating seeker detonating reactive armor was carried out.Furthermore, Then using the SPH model reconstruction method, the head jet after penetration of seeker is translated into 3D SPH calculation model, the pre-warhead jet detonation to ERA is performed by using SPH method.And the feasibility of the simulation results is was verified by an ERA detonation experiment.The results show that this calculation method can accurately predict the initiation ability of jet to ERA after penetrating the seeker.The clear material interface process of ERA detonation is got.Meanwhile, the process of detonating reactive armor with clear material interface was obtained.More importantly, it was found that The the ERA which is was detonated by the generated the precursor wave generated when the jet penetratesd the cover plate, andwhich proved .Tthe detonation theory of precursor wave ERA detonation is was proved.