The paper presents the construction technology for the underground diaphragm walls crossing public urban pipelines adopted in the construction of the open tunnels of Jinbin Light Rail Project. The paper expatiates on the construction steps of the underground diaphragm walls, i.e., pipeline reinforcement and construction of guide walls, principle of breadth division of underground diaphragm walls, slurry preparation, trench cutting process, fabrication and installation of rebar cages, concrete casting, etc. Due to the adoption of such construction technology, the construction of the open tunnels can be executed without the necessity to cut off the pipelines. The paper provides a brand new concept for similar works in the future.