The invention discloses a vehicle-mounted aromatherapy diffuser. The vehicle-mounted aromatherapy diffuser comprises a main machine housing, a vehicle charger head connected bracket, a motor, a fan, a main machine circuit board, an atomizer and a water tank; the main machine housing comprises a main machine upper shell and a main machine lower shell; the main machine upper shell and the main machine lower shell are both hollow structures, which are open at the top and the bottom; the lower end part of the main machine upper shell is inserted in the main machine lower shell; an accommodating space is formed between the external surface of the lower end part of the main machine upper shell and the internal surface of the main machine lower shell; and the main machine circuit board is mounted in the main machine lower shell and placed in the accommodating space of the main machine lower shell. According to the vehicle-mounted aromatherapy diffuser, as the vehicle charger head connected bracket is rotationally connected with the main machine housing in an integrated manner, the angle of the aromatherapy diffuser can be adjusted according to actual needs and the messy wiring mode of the traditional separated type vehicle charger bracket can be also changed so that interior spaces of vehicles are tidy; and moreover, through adoption of a connected (plugged) type design, the vehicle-mounted aromatherapy diffuser is convenient in use.