The presence of minimum value of initiation impulse in K-I curve is proved by the examination of firing current(I) and initiation impulse(K)of commercial electric detonators.The definition of initiation impulse involved in the standard GB8031 is further supplemented;the importance to define the term of indexes of minimum initiation impulse and maximum no-fire initiation impulse is suggested,and the reason is elucidated that the value of firing probability should be changed from 99.99％ into 50% during measuring the firing current in 100ms with up-and-down method.