In order to solve the technical difficulties to reinforce the deep marine soft soil foundation that including walkway network, the reinforcing technology by plastic drainage plate and sand column combined with surcharge preloading is proposed to reinforce the large scale complex deep marine soft soil foundation. The mechanical behaviors of the reinforced soft soil foundation during embankment filling and preloading are studied including the surface settlement and deep settlement characteristics, the excess pore water pressure dissipation mechanism, and the horizontal displacement law by field tests. The results show that the construction method used to reinforce the deep marine soft soil foundation has achieved good reinforcing effects. The settlement of the deep marine soft soil foundation accomplished mostly during the period of filling and preloading, which effectively reduce the post-construction settlement and construction period. The results provide an important reference for the reinforcement of the complex deep marine soft soil foundation. The settlement versus time curve of the marine soft soil foundation treated with plastic drainage plate and sand column combined with surcharge preloading is multistage development model. The settlement at the site reinforced by sand column is less than that at the site reinforced by plastic drainage plate. Meanwhile, the excess pore water pressure at the site reinforced by plastic drainage plate is greater than that at the site treated with sand column. The drainage effect of the upper soft soil is significantly superior to the lower. The top soil of the soft foundation under surcharge preloading would move to the treated area; while the soft soil below the surface 3 m would be pushed outside the region treated with plastic drainage plate and sand column.