Abstract: It is crucially important to prevent improper slurry pressure which results in blowing out of slurry from ground surface due to fracture and collapse of cutting face during slurry shield tunneling in cohesive soil. Slurry fracturing ground has its occurring and developing process and the hydraulic fracture phenomenon is difficult to totally grasp in the laboratory because of small sizes of samples, and the occurrence of slurring fracturing ground in actual ground is different from that in laboratory. To master the occurring and developing mechanism of slurry fracturing ground, in-situ deep hole tests are done by using self-made experimental instruments. The tests exhibit the process of slurry fracturing and extending. Based on the analysis of test results, the formulae to compute the slurry fracture extending pressure and speed are drawn, and the empirical formula of the extending liquid is generalized.