Abstract: According to the latest experimental results of HPM effect on digital electronic devices, a relation between the HPM pulsewidth(PW) and the upset threshold(UT) of effect obiect is sumaried. The relation suggests that UT decreases with the increasing of PW as the other factors are fixed, wheras, there is a inflection region of UT while PW increasing. The UT changes slowly when the injecting PW is greater than the PW corresponding to the inflection region.