Abstract: To effectively solve the problem of difficult drainage in substations, reduce power grid failures caused by accumulated water entering equipment such as cable trenches and terminal boxes, and effectively improve the reliability of power supply in the power grid. This paper analysis of the current reasons for poor drainage and severe water accumulation in cable trenches in substations, based on the principle of dual float ball monitoring "water level difference", a new drainage system combining the main and auxiliary water collection tanks is designed, which can not only ensure that the pump is not damaged due to frequent startup and heating, but also prevent the pump from being blocked by a large amount of debris in the water collection well. At the same time, this paper making the system a modular device is convenient for on-site installation and use, and this device has certain promotion value.