World Class Manufacturing is a management philosophy that emphasizes on meeting external and internal customers’ needs and expectations and importance of doing things right for world market society. One of the most world class production techniques is Just in Time (JIT). JIT production system has some components that need to implement it. Researches show that implementation of this system isn’t unique in all time, places and circumstances. Implementation of this system may be differed from one company to another and the components those are needed to a company may not be necessary in another company. The purpose of this study is to introduce a mathematical method for identifying elements and components that are critical for JIT success in different circumstances. The study recommends this method by using TOPSIS and Pareto techniques. We use TOPSIS and Pareto techniques for setting a priority and thereby selection of component and use entropy method for giving coefficient to TOPSIS matrix. In this process, the statistical population to answer these questions is 1500 of the company’s managers and engineers as experts in appliance industry of Iran. In this case we have extracted 5 components from 11 possible components in this system to implement in these companies (in appliance industry).The components for JIT implementation are different in different industries and companies. In a scene, while JIT implementation flow the logical priorities as an algorithm, it can perform regarding to its circumstances, readiness and needs. Concerning these circumstances, readiness and needs, these components of JIT must be implemented with priority in these companies: JIT supplier management, Preventive maintenance, set up time reduction, Lot sizing, Pull production system. Keywords: World Class Manufacturing, Just in Time, TOPSIS method, Pareto technique, Entropy method.