This paper has studied a kind of flexible production line scheduling problem with the objectives of minimizing the tardiness and increasing the use ratio of devices. The executed sequence of operation tasks was determined by their priority which was computed by dispatching rule with multiple constraints. The dispatching rules were optimized by means of Genetic programming algorithm, then complete the whole scheduling scenario by using the optimal dispatching rule. The result of simulation experiment shows that using GP algorithm to solve the production line scheduling problem is effective.