由于启动压力梯度概念的引入，渗流力学便有了动边界的概念。为了深入了解动边界的性质，该文根据理论分析方法对启动压力梯度存在时的地层压力传播问题进行了研究。研究发现，启动压力梯度存在时地层被分成流动区和非流动区，二者之间的界限为动边界。但是，由动边界概念出发，可以得出非流动区的流体既流动又不流动的悖论，因而理论已不能自洽。动边界由启动压力梯度引起，启动压力梯度并不存在，是一个实验假象，因而，动边界也不存在。消除动边界，渗流力学理论则能够自洽。

Starting pressure gradient introduces a new concept-moving boundary-into the flow in porous media. In order to clarify the property of moving boundary, a theoretical study is conducted on the pressure propagation in reservoirwith starting pressure gradient. According to the study, a reservoir can be divided into two zones: flowing zone and non-flowing zone, while starting pressure gradient exists. The division between the two zones is called moving boundary. Howeverfromthe moving boundary, a paradox comes out that the fluid in non- flowing zone can flowand can not flowsimultaneously. Flow theory in porous media can not be self-consistent. Moving boundary comes fromstaring pressure gradient. But staring pressure gradient is not existing and just a misleading experimental phenomena. So moving boundary does not truly exist. Removal of moving boundary makes the theory of flow in porous media selfconsistent perfectly.