In order to reveal the mechanical nature of granular cushion and deeply investigate the effect of granularcushion on the performance of rigid- pile composite foundation,a finite differential- particle flow (FDM- PFM) cou-pling method is proposed,and a coupling model for the static loading test of a single rigid- pile composite foundationis set up.Then,the calculation results are compared with the in- situ test results of a composite foundation of ahigh- rise building,with good accordance being found,which means that the proposed coupling method is effective,and that the macro and micro parameters are properly selected.Finally,further simulations are performed to ana-lyze the effects of different cushion materials on the properties of rigid- pile composite foundation.The results showthat (1) with the increase of cushion stiffness,the settlement decreases,the pile- to- soil stress ratio increases,andthe penetration of the pile top into the cushion decreases; (2) the range of negative skin friction area of the pile isdetermined as follows: 0.30L of medium and coarse sand,0.25L of crushed stone,and 0.20L of graded sand andstone; and (3) with the increase of cushion stiffness,the negative skin friction decreases,while the axial force ofthe pile increases.