Provided are a maintenance-free gas density relay and a mutual check method therefor. The maintenance-free gas density relay includes a gas density relay body and first gas density detection sensors which are in communication on gas paths, and an intelligent control unit connected to the gas density relay body and the first gas density detection sensors separately, where the intelligent control unit compares and checks a first pressure value and a second pressure value acquired at the same gas pressure, and/or compares and checks a first temperature value and a second temperature value acquired at the same gas temperature, or compares and checks a first density value and a second density value acquired at the same gas density, and can further upload received data to a background for data comparison by the background. The present disclosure further completes online self-check or mutual check of the gas density relay while being used for monitoring gas density of a gas-insulated or arc-control electrical apparatus, thereby improving efficiency, avoiding maintenance, reducing cost, and ensuring safe operation of a power grid.