A new demand rate expression closer to reality is presented considering the influence of both price and the time when the products apart from factory. With dynamic pricing policy, the profit function of an inventory cost model is established. Exact holding cost model is also investigated. Because of the complex form of the function, the properties of the profit function are analyzed by using genetic algorithm. The relationships of the optimal profit and the optimal price and repricing time are given. And the affects of changing holding cost and consumers desire to purchase are also investigated.