The castinsitu reinforced concrete and plastic concrete antiseepage system are adopted for support and antiseepage system of dry dock of Honggu Tunnel in Nanchang in waterrich sandy stratum adjacent to river based on numerical calculation of slope support and drainage simulation of inner dry dock. The multiple drainage tests and flood season show that the support and antiseepage system adopted for dry dock slope is reliable, adaptable, convenient and with good prevention effect, low cost and little maintenance work. The study can guarantee the construction schedule of the tube prefabrication and even the project.