Abstract: This article performed fracture toughness testing on L245 pipeline steel in hydrogen environment containing with different gas impurities, comparatively studying the influence of gaseous impurities on the fracture toughness of L245 pipeline steel in a hydrogen-containing 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 fracturing in air, L245 exhibited a brittle initiation of cracking in 4 MPa H₂ environment, with a decrease in the characteristic values of fracture toughness by 6.5%. as for Adding 100 ppm H₂O 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%. as for 4 MPa H₂ +100 ppm H₂O environment, the addition of CO₂ can 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 faracture 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.