Both Chinese Dialecticians and Western Sophists are wonderful work in the history of logic in the world. They are same in paradox expression of speech, double arguments in thinking way, and reductio ad absurdum argument to refute way. The doctrine of the Dialecticians and the Sophists is a precursor and stimulate to logic, and logic is a screening, modification and sublimation to their doctrine. The unity of opposites between the Dialecticians' and Sophists' theory and logic provides a driving force for development to logic. There are important philosophical and cultural significance to analyse the contradiction between the Dialecticians' and Sophists', theory and logic to reveal the mechanisms and laws of logical development.