According to some data, the author argues that back-arc spreading may be caused by tongue end of plate tongue. Differentiation by liquidation takes place on tongue end, which is low thermal conductivity and maybe have some form faults. Lower dense part would rise up and dilate, while high dense part would sink. Thus convection would work. Under proper conditions, it would cause back-arc spreading. This model can be also successfully used in archipelago. And most important, it can draw us a picture on cycle of back-arc spreading. According to some data, the author argues that back-arc spreading may be caused by tongue end of plate tongue. Differentiation by liquidation takes place on tongue end, which is low thermal conductivity and maybe have some form faults. Lower dense part would rise up Under proper conditions, it would cause back-arc spreading. This model can be also successfully used in archipelago. And most important, it can draw us a picture on cycle of back-arc spreading.