Abstract: Disclosed are an arc discharge detection method and device for a battery system, and a battery energy storage system. The arc discharge detection method for a battery system comprises: sampling a terminal voltage and a charging and discharging current of a battery system, sampling the terminal voltage of the battery system twice and calculating a first voltage difference value, and sampling the terminal voltage of the battery system and a terminal voltage of an electricity load and calculating a second voltage difference value; performing time domain and frequency domain analysis on the sampled data to obtain corresponding time domain and frequency domain feature values; and on the basis of the time domain and frequency domain feature values and the first and second voltage difference values, determining whether arc discharge features are met, so as to determine whether an arc discharge fault occurs in the battery system.