According to the characteristics of the pit supporting in Suzhou Center project, which is near the subway and severing the confined water, ultra deep underground continuous wall was adopted to brace the foundation pit. Aimed to the engineering key, difficult point and the quality control requirement, the research and analysis were made on the slurry in groove constructing process for the ultra deep underground continuous wall. A whole set of slurry preparation, parameter control and slurry treatment were presented. The practice showed the slurry is very feasible in the underground continuous wall engineering.