The construction of the lock chamber on the deep soft ground can affect not only the project duration and cost, but also the project quality and later maintenance. This paper expounds in detail the soft ground treatment of the lock chamber, the bottom form of chamber wall and form brace, and the controlling of perpendicularity, etc. It reveals the preconditions of complicated foundation in the construction of the lock chamber: proper organization, strict execution, timely monitoring and survey, as well as scientific analysis and decision.