The invention discloses a grass trimmer. The grass trimmer comprises a grass trimming head; a driving device for driving the grass trimming head to be rotated to cut plants; and an operating device operated to control the grass trimmer by a user. The grass trimming head comprises a thread spool and a head housing. The thread spool is used for winding a grass trimming rope. The head housing is used for containing the thread spool and forming a thread hole through which the grass trimming rope passes. The driving device comprises a motor. The grass trimmer has an automatic winding mode. Under the automatic winding mode, the motor drives at least one of the thread spool and the head housing to enable the thread spool and the head housing to be rotated relatively, so that the grass trimming rope is automatically wound on the thread spool. The provided grass trimmer has the automatic winding mode, and is capable of enabling the grass trimming rope to be automatically wound on the thread spool under the action of the motor.