Firstly, the paper presents the status of the research of circulating pressure loss. Then the mechanism of shear thinning property is analyzed. With the example of Bingham fluid, the checking results of software calculation and engineering examples demonstrate that the critical ratio of yield point to plastic viscosity (YP∕PV) is corresponded with certain engineering conditions and apparent viscosity. The circulating pressure loss with the critical YP∕PV ratio is the least. Laboratory tests and software calculations indicate that improving mud lubricating ability and solids control technologies are also effective technologies of decreasing circulating pressure loss.