Abstract: In this paper，the definition of theoretical relative deviation from Γ-information is introduced in two-valued propositional logic.Meanwhile the conditional truth degree expressions are showed and a new conclusion mode that the formula derived from theoretical relative deviation is the 3-typical error of less than ε in the abstract is put forward.At the same time the equivalence relations are proved among the conclusion modes for the 1，2-typical errors of less thanε.These studies can diversify research means of the approximate reasoning problems in two-valued propositional logic system.

摘要： 在二值命题逻辑中引入了信息Г下理论的相对偏差概念，给出了相对偏差的条件真度表示式；提出了由信息Г下理论的相对偏差确定的公式是理论的III-型误差不大于ε的结论模式，并证明其与I，II-型误差不大于ε的结论模式是等价的，为从不同角度研究二值命题逻辑中基于条件真度的近似推理问题提供多样化工具。