Then the mechanism of consolidation of double-layered ground improved by surcharge preloading method is analyzed, and a method to calculate the excess pore water pressure in the double-layered ground under the condition of staged loading or unloading is deduced. 分析了双层地基超载预压的固结、沉降机理,给出了多级等速加、卸载条件下双层地基一维固结孔压解析解。