Heptafluoro-isobutyronitrile (C4F7N) is a novel environmentally friendly insulating and arc extinguishing gas utilized as a replacement for SF6 in gas insulated equipment (GIE). Nevertheless, the potentially hazardous decomposition byproducts of C4F7N resulting from sudden equipment failure may jeopardize the normal operation of GIE and the physical well-being of the operator. In this paper, using the first principles study the adsorption behavior of four common C4F7N decomposition gases (CF4, COF2, CF3CN, C2F5CN) on PdSe2 monolayer, and explore the adsorption mechanism of PdSe2 monolayer on C4F7N decomposition gas. The results show that the PdSe2 monolayer interacts with the four decomposition gases by physical adsorption mechanism, in which the PdSe2 monolayer causes the largest change in electronic properties and maximum work function (0.15 eV) near the Fermi level before and after adsorption of C2F5CN, indicating a strong interaction between C2F5CN and PdSe2 monolayer. The sensitivity of PdSe2 monolayer to C2F5CN was up to 68.61 %. Therefore, PdSe2 monolayer has the potential of selective detection of C2F5CN gas sensing materials, and the findings in this paper provide theoretical guidance for the development of PdSe2 monolayer gas sensing sensors for monitoring C4F7N insulation equipment.