The problem of determining the sequence of a set of jobs with the objective function (OF) for minimizing the maximum earliness and tardiness, is studied. Since this OF is trying to minimizing and diminish the values of earliness and tardiness, it corresponds to different production systems, such as jIT. This OF is studied in problems associated with m machine and n jobs in Flow Shop case (n/m/P/Etmax).Several methods have developed for solving Flow Shop problems. Two quick heuristic methods, called HI and H2, with the aim of finding proper solutions in short time, are suggested. The branch and bound (BB) optimal method for solving n/rn/P/ETmax problems is applied. Offering fair upper and lower bounds results in obtaining optimal solutions in many problems. 400 n/rn/P/ETmax problems of small, medium and large sizes are randomly generated.For 83% of problems, optimal solutions are obtained, by BB method. The associated ranges for these problems are 4 to 75 machines and 4 to 50 jobs.