Abstract: It was studied the surface settlement,excess pore water pressure,deep settlement and lateral displacement etc,as well as improving effect of thick soft subsoil below large overburden treated by vacuum combined surcharge preloading,according to monitoring and detection data on site.The results showed that the curve of surface settlement was smooth and there was no obvious gradient change section during high fill preloading,because of stress diffusion of the overburden.The compressive deformation of subsoil occurred mainly in the soft soil layer below the overburden,and the increase and dissipation of the excess pore water pressure were offected by the co-action of vacuum pressure and filled preloading,which were related to the thickness of the overburden.When the overburden was thin,it had a faster response,so the value of the excess pore water pressure by preloading was larger;when it was thick,the value of the excess pore water pressure was smaller.Hence,it is unfavorable to drainage and improving of a soft soil in case of existing overburden,to which attention should be paid in the design and construction of a project.