A heating, ventilating, air conditioning (HVAC) system of a vehicle includes: a battery circulation line having a battery radiator, a main valve, a high voltage battery core, and a cooling heat exchanger so as to circulate a first coolant therethrough, with the cooling heat exchanger being provided to be heat-exchangeable with an indoor HVAC refrigerant line; a branch line including a water heating heater and selectively connected to the battery circulation line through the main valve; and a controller selectively cooling or heating the high voltage battery core by controlling an operation of the main valve, the water heating heater, and the indoor HVAC refrigerant line.