Characteristics of six M-components with peak currents of kilo amperes are analyzed by using the data from the artificially triggering lightning experiment in Shandong 2009, including the current at the base of the discharge channel, the surface electric field change at 30 m from the channel, and the high-speed camera records. The M-component is associated with the abrupt enhancement of channel luminosity with a duration of less than 1ms. Both the current and electric field are characteristic of relatively symmetric waveforms with a rise time of several tens of microseconds. The simultaneous records show that the electric field starts to change and reaches its peak earlier than the channel base current. Because of the obvious continuing current flowing in the channel, the conductivity of the discharge channel prior to the M-component is better than that prior to the leader-return strokes. The channel condition before the occurrence of the M-component is crucial to current amplitude and rise time. According to the waveforms of current and electric field recorded simultaneously, it is inferred that the M-component evolves from up to down and the evolvement continues after contacting the ground, and then an upward reflected process is induced. Further analysis shows that the interaction between these two processes is likely to be changed with altitude.