The current parameters of asymmetrical current breaking of a generator circuit breaker are calculated with the DC time constant of 150 ms via Microsoft Excel and dichotomy.By analyzing the alternative and direct components

the current formula for last-pole-to-clear condition is derived.According to the calculation of the current parameters and the comparison between the standards IEC 62271-37-013 and GB/T 1984 —2003 for generator circuit break（GCB） asymmetrical current tests

it is concluded that the IEC 62271-37-013 under discussion is more reasonable as it takes the current parameters for last-pole-to-clear condition into consideration.