Taking the mud as non-Newtonian fluid, the leakage of the cofferdam in different positions for emergency repair of buried pipeline in mud flat was studied using ANSYS Fluent software. The influence of non-Newtonian consistency coefficient, power law index, and gap size on leakage was discussed, and the hourly rise of mud in the cofferdam was calculated. The results indicate that when the power law index is less than 1, shear thinning occurs, and the apparent viscosity of mud decreases with the increase in shear strain rate. With the increase in power law index, the leakage increases gradually, indicating that the apparent viscosity decreases with the increase in power law index. Moreover, when the power law index is greater than 1, the leakage increases further, indicating that the shear strain rate is less than 1 during flow process. The leakage of the cofferdam decreases gradually with the increase in consistency coefficient, but increases significantly with the increase in gap size. When the power law index is in the range of 0.3 to 0.5, the consistency coefficient is in the range of 3 to 9.kPa·s, and the gap size is in the range of 5 to 10 mm, the total height of the mud rising inside the cofferdam has little effect on the construction inside the cofferdam.