After the first and second return strokes (RSs) of a multi-branch triggered lightning flash, the M component of two different initiation mechanisms burned: (1) Upward leader (UL)-M component, (2) Downward leader (DL)-M component. The UL-M component burned immediately after the RS (about 0.5 ms after the RS). At this time, an UL developing to the cloud generated outside the main channel of the continuous current (CC). With the development of the UL, the M component is formed in the CC channel. The obvious DL process can be observed during DL-M component. The speed of DL is about 2 × 107 m/s, when DL was intercepted by CC channel, M component will generate. The current peak and electric field peak of the UL-M component were larger than those of the DL-M component. It was worth noting that the M component formed by the UL slightly developing to the ground at the head of it did not produce an electric field change at the observation point 2 (1550 m horizontally from the rocket triggered lightning point), which was a result of the combined effect of the positive charge in the branch head and the negative charge in the main channel at the same height. The reflection phenomenon of the M component was also observed in a DL-M component process. The CC in the channel after the RS plays a key role in the formation of the M component. It forms the M component by intercepting the current wave transmitted to the ground from the cloud or the lightning branch. •High-speed camera data shows the M component of two different mechanisms: (1) Upward leader -M component, (2) Downward leader -M component.•Continuous current channel intercepts the charge to form M component.•The current peak and electric field peak of the UL-M component were larger than those of the DL-M component.