Abstract: Identical parallel machine earliness/tardiness scheduling problem with common due-date is studied. A kind of hybrid genetic algorithm is presented to determine the common due-date ,job code, and processing orders of every processed job on each machine, that is, find an optimal common due-date and optimal scheduling policy for minimizing the total cost of assignment of due-date, early delivery and tardy delivery. Numerical computations show that the hybrid genetic algorithm has advantage over heuristic procedure ,and is fit for larger scale identical parallel machine earliness/tardiness scheduling problem. The algorithm proposed has low computational complexity and strong robustness.