Mixed-model-assembly-lines (MMAL) are widely used in modern industries. There are two principal kinds of industrial organization patterns, which called the United States Pattern and the Japan Patter. The Japan (Toyota) Pattern will be studied in this article and the objective of this pattern is minimizing the stoppage and the idle time. Genetic algorithm is been used for solving the problem and more than 5000 examples have been designed. The results will shown the better parameters for the assembly line and the genetic algorithm.