This paper is focused on the problem for one-by-one products input into Flexible Transfer Line (FTL) and describes the research of an off-line production simulator connected Genetic Algorithm (GA) system in order to search a better solution. New individual expression, crossover operations, mutation operations in GA and their application examples are also described. When a single FTL manufactures a variety of products, there is a problem to keep a production rate called production levels. The developed production simulator connected GA system to have a wide solution search space can solve the problem for production levels. The relation between a production simulator and GA system is that GA system generates some of the input information to operate a production simulator.