The present invention provides an amorphous silicon thin film transistor and a manufacturing method of the amorphous silicon thin film transistor, which comprise: a substrate, a gate electrode layer, a gate insulating layer, an active layer, a source/drain electrode layer, an N+-doped layer, a protective insulating layer, and a passivation layer. The N+-doped layer is disposed between the active layer and the source/drain electrode layer. The protective insulating layer is disposed on the source/drain electrode layer. A channel is formed in the source/drain electrode layer and penetrates the N+-doped layer and the protective insulating layer. The passivation layer covers the channel and the protective insulating layer. The protective insulating layer and the source/drain electrode layer are flush with each other in the channel.