Tadong iron deposit is the largest submarine volcano plume - metamorphic - reformation iron deposit in Jilin-Heilongjiang metallogenic province. The geological characteristics, geochemical characteristics, electron-probe analysis and Re-Os dating of pyrite in the deposit were reported for the first time in this paper. The deposit occurs in ore-bearing rocks of Tadong Group. The ore bodies show structures banded, lamellar banded or lenticular-like structures. The attitude of the ore body is consistent with surrounding rocks. The banded structure is a main ore structure, secondary layer laminae, compact block, and crumpled structure and so on. Geochemical data display that Tadong iron deposit was formed in the alternative depositional environment of submarine chemical deposition - submarine basic volcano eruption - submarine volcano clastic deposition. The deposit has characteristics of SEDEX type deposits. Its tectonic environment is arc tectonic environment of continent to continent collision zone. The major element content of magnetite in Tadong iron ore FeOT values are 88.49%~93.72%, average 92.35%, SiO2 values are 0 ~ 1.058%%, average 0.075%. TiO2 values are 0 ~0.13%, average 0.03%. Al2O3 values are 0~ 0.30%, average 0.06%, MnO values are 0~ 0.08%, average 0.03%. TiO2 values are 0 ~0.13%, average 0.03%. Genetic types of inmagnetite in Tadong iron ore include magmatic rock type, volcanic rock type, and sedimentary-metamorphic type. The major element content of pyrite in Tadong iron ore Fe values are 43.534%~48.246%, average 46.779%, S values are 48.728%~54.402%, average 51.837%. S/Fe values are 1.782~2.072, average 1.931. The values belong to the sulfur week depletion type. The trace element content of pyrite in Tadong iron ore Co values are 0.039%~0.573%, average 0.143%, Ni values are 0.008% ~ 0.502%, average 0.077%. Co/Ni values are 0.165~19.759, average 4.04. The deposit has the characteristics of volcano hydrothermal and metamorphic hydrothermal iron deposit. Five samples of pyrite for Re-Os isotopic dating are analyzed and W ( Re ) range from 1 172× 10-12 to 29810× 10-12 , w ( Os ) range from 20× 10-12 to 184×10-12. 187Os/188 Os range from 3.82 to 52.11, 187Re/188Os range from 601 to 7 739. The model ages value from 370Ma to 448Ma, Corresponding isochron is 401± 41Ma, MSWD=10.2, Initial187Os/188Os is 0.3± 3.4. Higher 187Os/ 188Os and γOs(t) value suggests that the ore-forming materials originated from the crust .The age is indicated that the Tadong iron deposit was formed in the late Caledonian. Ore-bearing rock series were formed in the early Palaeozoic, but not were formed in late Proterozoic.