Disclosed herein is a waste heat management system of an electric vehicle. In particular, a pump for controlling the flow of cooling fluid, an OBC cooling fluid line and a motor cooling fluid line which diverge in parallel from an outlet of a cooling fluid line of the fluid pump, and a heater core cooling fluid line and a radiator cooling fluid line which are respectively connected in parallel with a junction of an inlet of the fluid pump cooling fluid line and a junction of outlets of the heater core cooling fluid line and the radiator cooling fluid line, are interconnected to provide both heating and air-conditioning to the interior of the vehicle. Additionally, the present invention, also allows the motor to be preheated when the vehicle is not running.