Deduced from caisson method, this article puts forward, a new method of constructing underground pipe in densely built area the Sinking Trough method.

The paper compares the methods dealing with water leakage from trough bottom of water-sealed gasholder, and introduces the construction way and effect of excavation method.

During programming for the trough and cavity, programming of arc method is used for some typical positions of trough and cavity to improve the machining precision.