The coherence of two-level atom in a thermal radiation field without rotating wave approximation through an external controllable driving field was investigated. The time evolution properties of non-opposite angle element of two-level atom's reducible density rectangular array was discussed. Coherence properties of two-level atom was studied in degenerate two-photon processes when the two-level atom interacts with an driving field in the thermal radiation field . We obtained the properties of an external driving field when two-level atom's coherence is maintained.