Abstract: The characters of 7.5 a timing series of dual-frequency timing for millisecond pulsar PSR J1939+2134 are studied for the first time.DE421 is suggested by analyzing the effects on the precision of pulsar timing with different planet ephemeris.The long-term stability of pulsar time and that of atomic time is evaluated using σz(τ) method,and it is found that the long-term stability of pulsar time is always improved with time elapsed and up to 10-15 in 6 a.Hence,pulsar time has obvious advantage as the time standard for keeping time and time service.