The invention discloses a low-voltage lightning arrester with a built-in disconnector, and belongs to the field of lightning arresters. A built-in hot melting separation component is arranged in the low-voltage lightning arrester, a low-temperature hot melting mode and a quick separation structure are adopted, heat generated by a valve plate/a resistance plate when the low-voltage lightning arrester fails is fully utilized to melt a hot melting medium in a working rated voltage range lower than 1kV, initiating an action of a pressure storage spring, and further achieving a function of an automatic hot melting type separation of a fault lightning arrester from the system on the low-voltage lightning arrester so as to prevent a further expansion of accidents. On the other hand, an obvious visibility mark can be given to the low-voltage lightning arrester which exits from the fault so that maintenance personnel can find fault points in time for maintenance and replacement. When the resistance plate in the low-voltage lightning arrester is about to thermally collapse, and short-circuit current is about to generate a front action, a damaged lightning arrester exits the system, and accidents caused by the short-circuit current are avoided. The low-voltage lightning arrester with the built-in disconnector can be widely applied to the fields of design, manufacture, operation, maintenance and the like of the low-voltage lightning arrester with a working voltage from 1kV to below 0.5kV.