中文摘要：

证明了年龄更换策略和成批更换策略依矩母函数序减少（增加）任意时间间隔内的失效次数的充要条件是基分布具有NBUMg（NWUMg）性质；更换间隔不同的成批更换策略在相同工作时间内的失效次数也作了比较。

英文摘要：

It was shown that both the age replacement policy and the block replacement policy would decrease（increase） , in the sense of moment generating function order, the number of failures in any time interval if and only if the underlying distribution possesses NBUMg （NWUMg） property. The stochastic comparisons of the number of failures under the block replacement policy with different intervals were made as well in this paper.