Vehicle heat pump system and control method therefor

Disclosed in the present invention is a vehicle heat pump system capable of improving dehumidification performance by increasing the flow of a refrigerant toward an evaporator during heating and dehumidifying modes. The vehicle heat pump system comprises: a bypass line which branches off between a first expansion valve and an outdoor heat exchanger and bypasses through the outdoor heat exchanger and the evaporator; a first refrigerant flow control valve for adjusting the opening degree between the bypass line and a refrigerant line toward the outdoor heat exchanger; a dehumidification line branching off between the first expansion valve and the first refrigerant flow control valve to supply the refrigerant to the evaporator; and a control unit for controlling the amount of refrigerant supplied to the dehumidification line according to outdoor air temperature or compressor RPM.