本文对逐步增加Ⅱ型截尾下指数分布场合恒定应力加速寿命试验进行了统计分析，得到参数的最大似然估计存在唯一的充要条件。最后通过模拟例子表明最大似然估计是有效的。“,”In this paper, we obtain the necessary and sufficient condition of the existence and unique- ness of maximum likelihood estimation for the constant stress accelerated life tests for the exponential distributions under progressive Type-Ⅱ censoring. We demonstrate through an simulation example that the maximum likelihood estimation is efficient