Accurately evaluating missile products with the characteristics of "long-term storage and one-time use" is a prerequisite and key to achieving safe storage， reliable use， and reasonable maintenance， which has significant military and economic benefits. However， existing storage reliability evaluation methods do not consider the phenomenon of "upside down" and incomplete data of missile products， resulting in low evaluation accuracy. According to the three characteristics of missile product life data， a minimum Chi-square estimation method based on order preserving regression is proposed in this paper. First， isotonic regression method is used to solve the problem of "upside down" in stored information. Then， the storage reliability is evaluated by the minimal Chi-square estimation method， and the goodness of fit is determined based on chi-square statistics. Finally， using the missile to store information naturally， the traditional method is compared with the method established. The results show that the establishment method significantly improves the rationality and accuracy of missile storage reliability evaluation and lays a foundation for scientific life determination and maintenance of equipment products.