The invention discloses a flow battery negative electrolyte solution sealing system and a flow battery system. The flow battery negative electrolyte solution sealing system comprises: an organic matter layer disposed on the negative electrolyte solution in a negative storage tank; a first pipeline connected to the negative electrolyte solution outlet of an electric pile and the negative storage tank, with one end of the first pipeline connected to the negative electrolyte solution outlet of the electric pile and the other end placed in the negative electrolyte solution; and a second pipeline connected to the negative storage tank and the negative electrolyte solution inlet of the electric pile. According to the invention, the organic matter layer is disposed on the negative electrolyte solution in the negative storage tank, and liquid state organic molecules have good fluidity and air tightness, thus ensuring good air isolation effect of the negative electrolyte solution to air, and the negative storage tank and a positive storage tank are connected by pipelines, thus ensuring the negative electrolyte solution in a safe liquid level state. Also compared with common flow battery systems, the capacity fading speed is reduced, and the flow battery system provided by the invention has good operation safety and stability.