中文摘要：

借助CPM网络计划进行工序机动时间特性研究是对项目进度进行科学管理的基础。针对项目进度中，若某工序的结束时间从最早结束时间开始一直推迟，其后继工序的机动时间是否会一直受其影响的问题，利用工序机动时间已有的概念和性质，提出路线机动时间和路线自由时差的概念，并借助这两个概念进行工序机动时间守恒性分析，得出某工序的后继工序的机动时间会在该工序的结束时间推迟到一定值后达到恒定值，不再随该工序结束时间的推迟而变化的结论，进而给出工序机动时间守恒性的充分条件，以及计算工序机动时问恒定值的方法。最后，通过应用举例进行具体分析和阐述。

英文摘要：

The study of float properties by CPM （Critical Path Method） network planning is the basis of scientific project schedule management. In project planning, when finish time of an arbitrary activity defers different value from the earliest finish time of the activity, the floats of its succeeding activities may be influenced. By means of the concepts and properties of floats, path float and path free float are presented. Based on the above two con- cepts, the analysis of activity float conservation is given. Furthermore, when finish time of an arbitrary activity defers some value from the earliest finish time of the activity, float of its succeeding activities may be invariable value. Moreover, enough-conditions activity float conservation is given, and the algorithm of invariable value is given. Finally, it is feasible and correct to use it through examples.