Disclosed are detection circuit and device of TRIAC dimmer and detection method. Detection circuit comprises line voltage sampling module, peak voltage sampling module, average voltage sampling module, judgment module, bleeder module, line voltage sampling module samples line voltage, outputs sampling voltage to peak voltage sampling module and average voltage sampling module; peak voltage sampling module outputs first comparison voltage to judgment module according to sampling voltage, average voltage sampling module outputs second comparison voltage to judgment module according to sampling voltage; judgment module compares first comparison voltage with second comparison voltage and outputs control signal according to comparison result to control connection or disconnection of bleeder module; bleeder module provides discharge current for TRIAC dimmer when being connected. According to invention, problem that detection result of TRIAC dimmer is unreliable can be effectively solved, and detection accuracy is improved.