Abstract: The activity float of network plan in a engineering cons-truction is the time kept in reverse for uti～lization of activity.There are some relations among the total float,the free float and the independentfloat.Studing their relations could help us in making and adjusting the plan and in controling theplanned engineering speed,and we can thus get much more in social and economical benefit.

Key words: network plan, float, utilization of float

摘要： 工程施工网络计划中的工序时差是工序可利用的机动时间，总时差与自由时差以及独立时差之间存在着内在的联系，研究它们之间的关系有助于我们进行计划的编制。调整以及在施工中对工程进度的控制，从而获得更大的社会效益与经济效益。

关键词: 网络计划, 时差, 时差利用