The monitoring components were put into the Shanghai-Nanjing intercity railway CFG pile-net composite foundation and Beijing-Shanghai high speed railway sand pile-net composite foundation of Kunshan test section, such as the soil pressure boxes, the settlement gauges and the pore water pressure gauges, etc., to monitor and obtain a large number of ground settlements(post construction), pile tops pressure and soil pressures, pore water pressures and other field test data in order to get variation law of properties of composite foundations. Working behavior of foundation during construction period and post construction settlement control effect were comparatively analyzed between the two different pile types (CFG pile-net and sand pile-net). The results showed that both CFG pile-net and sand pile-net preloading can meet the ballastless track of high-speed railway post construction settlement (less than 15 mm) control requirement according to the field tests. The total settlements and the velocity of settlement of CFG pile-net foundation were smaller than that of sand pile-net foundation, and its convergence speed was faster, which meant the latter requires a longer period of time to load. Affected by the pile stiffness, there was a big difference on the law of stress of pile and soil. The stress ratio of pile and soil in CFG pile-net foundation was increased with the increase of the filling of the embankment, and eventually stabilized, while that of sand pile-net foundation decreases with the increasing of load first, and then increase, presenting the wave shape change. And the CFG pile-net foundation excess pore water pressure dissipation rate was far less than the latter. In the case of short construction period, compared with the composite foundation of sand pile-net, the settlement control effect of CFG pile-net composite foundation treatment technology was more excellent.