A trimmer head includes a spool configured to rotate about a rotation axis. The spool is provided with a plurality of first transmission teeth. A head housing accommodates at least a part of the spool. The head housing is provided with a plurality of second transmission teeth for engaging with the plurality of first transmission teeth. When the trimmer head rotates about the rotation axis and along a predetermined direction, the plurality of first transmission teeth engage with the plurality of second transmission teeth to transmit force between the head housing and the spool. The force acts on a point of action of the head housing or the spool to drive the head housing and the spool to rotate synchronously along the predetermined direction.