Abstract: For constructing slurry shield tunnels under rivers or seas, it's a difficult technical problem to maintain the stability of the excavation face while preventing slurry fracturing. There are some laboratory investigations of slurry fracturing. But, due to small sizes and different boundary conditions, the results cannot be directly applied to the projects. In-situ slurry fracturing instrument is developed on the basis of theoretical analysis, and the test procedures of fracturing and the relevant method of confirming fracturing pressure are introduced. The in-situ slurry fracturing test is carried out on the rive-crossing tunnel under construction in Nanjing. The results indicate that: (1) as the fracturing process is a mutation process, the stratum fracturing model can predict fracturing pressure by means of the total stress method, which agrees with actual working condition. The theoretical results show that the fracturing pressure of tunneling model, which is almost equal to the lateral earth pressure, is smaller than that of the in-situ slurry fracturing test. It's efficient to increase fracturing pressure by increasing the slurry viscosity, however, the effect is limited; and (2) the upper limit value of slurry pressure set for preventing slurry fracturing is given according to the results of the in-situ slurry fracturing test. The in-situ slurry fracturing test is performed by shield machine after originating, and it may verify the accuracy of the prediction model to some extent.