The time evolution of plasma channel produced by ultrashort and ultra high power laser pulses in the air has been investigated. The theoretical model considers the recombinati on of free electrons, positive and negative ions, as well as the attachment and detachment of electrons on neutral molecules in the air under the interaction with the successive coming laser's pulses. The analytical solution of rate equations of the charged particles in the plasma channel has been found when the detachment laser intensity is constant. Calculations show that the lifetime of the plasma channel with an electron density higher than 1012—1013cm-3 can be extended to microseconds by using a detachment laser to suppress the attachment between el ectrons and neutral moleculars. In the case of same wavelength and average power, the detachment efficiency of a short pulse sequence with a high repetiti on rate is higher than that of a continuous detachment laser.