A method for detecting azimuthal angle of a heat source includes a preparing step and a detecting step. The preparing step includes: detecting a unit period (Tc) by rotating a target positioning portion through one circle, and aligning the target positioning portion with an aligning member. The detecting step includes: driving the target positioning portion to rotate. The position of the aligning member defines an initial azimuthal position. When an infrared signal emitted from the external heat source is transmitted into an infrared sensor via the target positioning portion, a transmitting time is defined as a time point (Ts) of the heat source, and an angle between the target positioning portion and the initial azimuthal position is defined as an azimuthal angle (⊖x) of the heat source, in which ⊖x=(Ts/Tc)×360°.