Ultrasensitive gas sensors have been fabricated depending on novel 2D materials. The adsorption behavior of diatomic molecules (H₂, HF, N₂, CO, O₂, and NO) on the 2D‐SnP₃ monolayer is investigated by utilizing first‐principle calculations for seeking the applications of sensing and detecting gases. H₂ molecule displays weak adsorption effects on the SnP₃ monolayer, while N₂, CO, HF, and O₂ show a moderate adsorption effect. NO molecule tends to chemisorb, resulting in a significant change transition for the electrical conductivity of the SnP₃ monolayer. The calculation results of adsorption energies, charge transfers, and work function indicate that the SnP₃ monolayer can be a promising candidate as a room‐temperature NO gas sensing 2D material due to its high selectivity, conspicuous sensitivity, and short recovery time. This study can guide the feasibility of using SnP₃ monolayer as a NO gas sensor in further experimental applications.