The equivalence between direct test and synthetic test of circuit-breakers is always a matter of interest to the people

and sometimes it iseven a matter of controversy. In this paper the’ author intends to give an intro-duction to some basic concepts of the equivalence. The statistic propertiesof the circuit-breakers and comparative testing methods involved in the equivalence are described briefly. The background of the established synthetic technique as an international standard is introduced

and finally some questions concerned have been discussed.