The lifetime of plasma channel induced by femtosecond laser in air is investigated by adding external high voltage electric field. The lifetime is extended three times when the voltage reaches 350kV/m in our experiment. Theoretical simulation and analysis show that impact ionization is enhanced and attachment effect is reduced in high-voltage electric field. Also, a sharper falloff in dissociative recombination rate will lead to a corresponding marked increase in the lifetime of the plasma channel. Both experimental and theoretical results prove the feasibility of adding external electric field in prolonging the lifetime of plasma channel in air.