Abstract: The existing process decision-making and optimization methods have some problems, such as insufficient automation and unstable results. In order to solve the optimal solution of machining process, proposes a decision-making reasoning method based on branch and bound method. This method comprehensively considers the cost, processing efficiency and other evaluation indicators, and controls the solution space in a suitable range through "branch", "Relaxation" and "pruning", which improves the efficiency of reasoning and operation. Through the application and analysis of specific examples, the feasibility, effectiveness and practical application value of the algorithm are proved, especially for the reasoning and decision-making of the optimal machining method of machining process, which has broad application prospects.