The utility model relates to a door lock which is improved. The door lock which is improved is mainly composed of a lock body, a lock head, and a lock button box. The door lock which is improved is characterized in that the lock body and the lock head are fixed together, and a length regulating component is added between the lock body and the lock head, when the door lock which is improved is installed, the extending out length of the lock head can be regulated according to the thickness of a door plate; an auxiliary switch is added inside the lock button box, when a key is normally used to open a door, the auxiliary switch does not act, only when the door is prized, the auxiliary switch acts, and an alarm device is started. Thereby, the defect that the switch of the general anti-theft alarm lock (device) often acts to easily cause bad contact is overcome.