A trimming head for use with a grass trimmer includes a spool for winding a cutting line and rotatable about an axis, a head housing formed with apertures for the cutting line to pass through, a touched element configured to be activated, a first driving member configured to drive the spool to rotate to send out the cutting line, and a first transmitting member configured to cooperate with a first driving member to receive a driving force of the first driving member. The trimming head has a sending mode in which a length of the cutting line extends without rotating the head housing.
