长度对其直径的比ｌ／ｄ不大的管路是常有的。在这样的管路中，如果流动是层流，则层流起始段对能量损失的影响是必须考虑的。笔者曾用过几本教材和参考书，其中对层流起始段的分析不大一致，有的不太明确，容易给使用者造成误解。所以笔者从压力变化的角度分析、推导其能量损失的计算公式，目的是对于计及层流起始段影响的管路能量损失的计算有一个较清楚的认识。 Pipes whose length to diameter ratio is not large are common. In such a pipeline, if the flow is laminar, the impact of the initial laminar flow on energy loss must be considered. I have used several textbooks and reference books, of which the initial analysis of laminar flow is not consistent, and some are not very clear, easy to cause misunderstandings to users. Therefore, the author analyzes and deduces the formula of energy loss from the perspective of pressure change. The purpose is to have a clearer understanding of the calculation of pipeline energy loss which takes into account the influence of the initial stage of laminar flow.