A system of calculating temperature may include: a motor including a housing having opened ends, a cover connected to the housing to close at least one of the opened ends, a shaft rotatably disposed in the housing and having one end which penetrates through a center portion of the cover, a rotor fixed on an exterior circumference of the shaft in the housing and the cover, a stator fixed on an interior circumference of the housing, and an air gap formed between an exterior circumference of the rotor and an interior circumference of the stator; an input portion receiving a real time input and a predetermined input; and a control portion establishing a thermal equivalent circuit using the inputs of the input portion and convection or conduction characteristics between constituent elements of the motor, and calculating a temperature of each constituent element using the thermal equivalent circuit.