Stock model of economical order batch is established under the objective of maximum total profit according to the hypotheses of constant demand rate.Based on these facts,the author suggests that the stock model of economical order batch is established under the objective of maximum total profit in system according to the hypotheses of demand rate's relying on selling price.From which one extended a model can be deduced.By using extreme-value theory,the model is proven mathematically and the method of solution is deduced for optimal order batch,optimal selling price and how to define optimal order cycle,and the sensitivity analysis has been made.One applied example is also given.