A writing method and erasing method of a fusion memory are provided, and the fusion memory includes a plurality of memory cells, and each memory cell of the plurality of memory cells includes a bulk substrate; a source and a drain on the bulk substrate, a channel region extending between the source and the drain, and a ferroelectric layer and a gate stacked on the channel region; and the writing method includes: applying a first voltage between the gate of at least one memory cell and the bulk of at least one memory cell, in which the first voltage is less than a reversal voltage at which the ferroelectric layer is polarization reversed, and each of the source and the drain is grounded or in a floating state.