The invention discloses a metal bidirectional sealing valve cavity safety relief device, comprising a main cavity arranged on a valve; wherein the main cavity comprises an overflow cavity which can be communicated with the interior of the valve cavity and a relief cavity which can be communicated with an external pipeline of the valve cavity, and a connection channel is arranged between the two cavities; one end of the overflow cavity is sealed, and the overflow cavity is internally provided with a resetting mechanism which can cause the other end to be communicated or separated with the interior of the valve cavity. The invention has simple structure and low cost, the device can be directly arranged in a valve open-close part, and fluid pressure abnormally rising in the valve cavity can be relieved into the pipeline again, thus being safe and environmentally friendly.