We propose a kind of dynamic reliability growth model. Firstly, by using the middle rank in statistical field and the data gathered in the practical tests, we can find the failure rate of different growth periods. And this technique can solve the small sample problems. At the same time, this technique embodies the dynamic modeling thoughts, so it can well describe the practical condition of the running system. Secondly, this model inherits the merits that is simple, direct, easy to value the references of traditional Duane model, on the other hand, it can be used in the multi-period or multi-environmental tests in which traditional Duane model can not be applied. Thus, this model can be widely used in engineering. Finally we give a simulating example in order to demonstrate how to use this model and test the correctness of the model.