The invention discloses a field detection device and system for achieving no maintenance of a gas density relay. The field detection device comprises a temperature adjusting mechanism and an intelligent control unit, wherein rise and fall of the temperature of the temperature adjusting mechanism are controlled by the intelligent control unit, thereby making the temperature of a temperature compensation component of the density relay rise and fall to complete the field detection of the gas density relay, and no maintainer is needed to operate on site, which achieves no maintenance of the gas density relay, and greatly improves the efficiency and reliable and safe running of power grids. The invention further provides a field detection method for supporting normal running of the field detection device above.