The geochemical characteristics of volcanic eruption vary greatly due to factors including the volcanic eruption sedimentary environment (including submarine eruptive environment and subaerial eruptive environment) and magmatic acidity. Therefore the accurate identification of volcanic eruption environment is an important geological basis for the evaluation of volcanic oil and gas reservoir properties. In this paper, based on the geochemical data of 58 samples of Upper Carboniferous igneous rocks from NiuquanhuNiudong structural belt, Malang sag, Santanghu basin. We use the ratio of Fe2O3 to FeO as the oxidation index and mathematical statistics method to cast points to identify the eruptive sedimentary environment of the Halgau Formation (C2h) and Karagang Formation (C2k) of the upper carboniferous according to its distribution characteristics. Statistics show that the oxidation indexes of the 34 samples of the Karagang Formation (C2k) range from 0. 55 to 5. 00 and the values are mainly concentrated from 1. 0 to 3. 0, indicating that the volcanic eruption sedimentary environment is complex and not a pure oxidation environment. From the vertical distribution of some single wells, the oxidation indexes have a tendency to increase significantly from bottom to top, indicating that the volcanic eruption sedimentation has gradually transited from a weakly reduced environment to a strongly oxidized environment. The 24 rock core samples of the Carboniferous Halgawu Formation (C2h) have oxidation indexes between 0. 25 and 0. 94 and the values are mainly concentrated in 0. 2~0. 4, indicating that the volcanic eruption sedimentation is in a simple oxygen- reduced environment. From the vertical distribution of a single well, the change of oxidation indexes influenced by the depth is not obvious, indicating that the volcanic eruption sedimentation has been little affected by the dynamic water environment and has a certain depth of water. The research used data of 108 volcanic samples in 10 different basins in China and fully considered the effect of acidity on the oxidation index of volcanic rocks to establish a volcanic eruption environment identification map based on the distribution characteristics of oxidation indexes corrected by magmatic acidity. We used the map to identify the volcanic eruption sedimentation environment of the collected 58 rock core samples. The result shows that volcanic eruption sedimentation environment of Karagang Formation (C2k) is complex, which is dominated by land eruption and deposition and featured by frequent water and land transition environment. The HaerjiawuFormation(C2h) volcanic rocks are of typical underwater eruptive origin and were deposited in a highly reductive environment with a certain water depth. The results accord with the previous results obtained by effective identification symbols including the characteristics trace element enrichment, quenched slag- like structure, unconformity and weathering crust, Marine fossils and filling cement.Under the reasonable correction and avoidance of various influencing factors,the method of volcanic eruption sedimentary environment identification based on the distribution characteristics of oxidation index has universal applicability, which can be applied to the ancient geographical environment identification of volcanic eruption sedimentary in different geological ages and different basins with different geological backgrounds.