Tianping Tunnel crosses non coal formations containing harmful gas. The harmful gas detection can not only depend on geophysical methods, and the cost would be increased and the construction period would be lengthened by carrying out a great deal of geological drilling work. In this paper, the storage range of harmful gas in a stratum is calculated and the position of harmful gas in further section is prediction by measuring thickness and attitude of strata, projection calculating relationship between tunnel and strata attitude and main tunnel prediction through inclined shaft, on the basis of position of existing harmful gas, thickness and attitude of strata and strike of tunnel and rock. And then little geological drilling work is conducted to verify the results. Good effect has been achieved and the results can provide reference for design optimization and construction organization of similar projects in the future.