The invention relates to a protection method for metallic earth fault clearance of a negative-electrode direct-current connecting wire under the circumstances of the battery negative electrode grounding of the energy storage power station. The protection method comprises the following steps that: a theoretical value of a direct current of a direct-current connecting wire is obtained by calculation and is used a reference; according to the theoretical value, a protection setting value is set by combining the current value of the direct-current connecting wire on the normal operation condition; and a direct current value of a protection installation position is detected and an actual direct current value is compared with the protection setting value, and whether protection is carried out is decided according to the comparison result. According to the invention, under-volume current protection is used. The simulation result demonstrates that a fault can be detected reliably and the protection motion can be prepared; and high sensitivity and high reliability can be realized even under the circumstances of transition resistance consideration. Therefore, the provided protection method is suitable for metallic earth fault clearance of the negative-electrode direct-current connecting wire under the circumstances of battery negative electrode grounding of the energy storage power station.