Abstract: In order to solve the problem of easy blockage and difficult cleaning of pressure measuring pipes in water conservancy projects, a new type of assembled pressure measuring pipe with double-layer structure (composed of inner pipe and outer pipe, in which the inner pipe can be pulled out for cleaning or replacement during use) was designed. The diameter of the new pressure measuring pipe was optimized, and the influence of the pipe diameter on the lag time of the water level measuring of the pressure measuring pipe was discussed through theoretical analysis and mathematical derivation. Theoretical analysis showed that a small change in the inner diameter had a limited effect on the measuring lag time. It is recommended to increase the outer diameter to about 100 mm for ease fabrication and installation. The engineering practice showed that the new assembled pressure measuring pipe can be successfully manufactured and installed by using the existing construction technology, and the pull-out design of the inner pipe was feasible. The research results can provide reference for seepage monitoring of water conservancy projects.