Abstract: This article performed fracture toughness testing on L245 pipeline steel in hydrogen environment containing different gas impurities, comparatively studying the influence of gaseous impurities on the fracture toughness of L245 pipeline steel in such as environment. Scanning electron microscopy (SEM) was utilized to observe the fracture surfaces of the test samples, analyzing the fracture modes of L245 steel in hydrogen environment with different gaseous impurities. The results indicated that, compared to the ductile fracture in air, L245 exhibited brittle crack initiation in 4 MPa H₂ environment, with a decrease in the characteristic values of fracture toughness by 6.5%. When 1‰ H₂O was added to the 4 MPa H₂ environment, due to the combined effects of competitive adsorption and adsorption dissociation by H₂O molecules, the characteristic value of L245 fracture toughness increases by approximately 3.9%. In the 4 MPa H₂ +1‰ H₂O environment, the addition of CO₂ could promote hydrogen embrittlement of L245 steel due to the local elecrtochemical hydrogen evolution effect of CO₂ +H₂O, resulting in a decrease in the characteristic value of fracture toughness by 13.5%. Conversely, the addition of O₂ significantly reduced the degree of hydrogen embrittlement of L245, with an increase in the characteristic values of fracture toughness by 13.5% due to the competitive adsorption of O₂.