The invention discloses a self-diagnosis system for a locomotive top ascending high-voltage alarm. The self-diagnosis system comprises a self-diagnosis instruction key unit (1), an MCU unit (2), a signal generating unit (3), a protective filtering unit (4), a scaling-up unit (5) and a comparator unit (6). The self-diagnosis instruction key unit (1) and the MCU unit (2) are connected, the input end of the signal generating unit (3) is connected with the MCU unit (2), the output end of the signal generating unit (3) is connected with a signal connecting line 1 of a high-voltage sensor, and a signal connecting line 2 of the high-voltage sensor, the protective filtering unit (4), the scaling-up unit (5) and the comparator unit (6) are sequentially connected. The tail end of the signal connecting line 2 of the high-voltage sensor, the output end of the protective filtering unit (4), the output end of the scaling-up unit (5) and the output end of the comparator unit (6) are each provided with a lead connected with the MCU unit (2). The invention further provides a self-diagnosis method for the locomotive top ascending high-voltage alarm, and a reliable means is provided for testing the sound condition of the locomotive top ascending high-voltage alarm for an operator before locomotive top ascending.