The technological measures to control oxygen content of gear steel in 100 t EAF⁃LF⁃VD⁃CC⁃CR whole process are put forward. The rotary bending fatigue properties， fracture and inclusion size of gear steel 20MnCr5 with oxygen content 0．000 53％ ~ 0．001 45％ are investigated. The results show that the higher the oxygen content， the larger the size of maximum inclusion and the lower fatigue strength of steel， while [O] ≤0．001 0％ ，with [O] decreasing， the fatigue strength of steel decreasing within a narrow range； the critical inclusion size of the test steel without fatigue crack under the surface is 21 μm and the shallow zone 30 ~ 430 μm away from the surface is relatively safe zone， where inclusions are difficult to cause fatigue cracking．