A streetlamp fault detection apparatus and a streetlamp fault detection method thereof are provided. The streetlamp fault detection apparatus is coupled to a streetlamp loop, and stores an impedance condition table defining a reference impedance range and a non-reference impedance range. The streetlamp fault detection apparatus measures a total impedance value of the streetlamp loop in a measurement period, determines that the streetlamp loop is in a normal operating state if the total impedance value stably falls within the reference impedance range in the measurement period, and determines that the streetlamp loop is in a fault state if the total impedance value falls into the non-reference impedance range in the measurement period.