Abstract：It is a key step for reducing waste generation in chemical processes to design optimal reaction paths. In this paper, a new conception of simple stoichiometric reaction is proposed for the reaction path synthesis problem. A simple stoichiometric reaction is the reaction in which the freedom of atomic matrix formed by reactants and resultants is 1 and also fulfils the atomic balance equations. The simple stoichiometric reactions greatly reduce the number of reaction equations, so as to reduce lots of search space in reaction path synthesis. All simple stoichiometric reactions can be obtained by mathematical transformation for atomic matrix of a reaction system, and the best one is then easily to be chosen. This conception is an important basis for much more complex problems.