The properties of long plasma-channel generated by terawatt (TW) femtosecond laser propagating in natural environmental air are investigated. It shows that the plasma filamentation with length of 2 km can be achieved when 2 TW femtosecond laser propagates in natural environment, and the electron densityis measured to be 1011 cm-3 at different location of filament, which shows the good conductivity of plasma channel even at the end of channel. Moreover, high voltage discharge test also confirms that, compared with the case without plasma channel, the high voltage of discharging can be reduced by 30% when plasma channel exists, which indicates the effectiveness of fs laser induced discharging. This work paves away for generation of several kilometer and long lifetime filamentation in air, laser induced lightning, environmental monitoring, and artificial intervention of climate.