A determining method for simplifying a compaction pile composite foundation calculation model comprises the steps that firstly, the total area of compaction piles is obtained through the designed pile number and the area of a single pile 1, the total area of a whole pile soil treatment area is obtained through design parameters, and the area replacement rate of a composite foundation can be obtained through comparison calculation of the total area of the compaction piles and the total area of the whole pile soil treatment area; secondly, equivalent serialization processing is carried out on disperse triangular pile distribution according to the principle that the area replacement rates are equal, the requirement for equivalence or similarity of the area replacement rate and the practical engineering is met by regulating the width of annular piles, the circle diameter of soil among central piles and the width of soil between every two annular piles, and a spacing arrangement calculating model for the soil of the annular pile and the soil between the piles is proposed; thirdly, a reasonable calculation boundary is intercepted on the periphery of the pile soil managing area, and a finite area is used for replacing an infinite area; fourthly, soil between the annular piles and the piles and peripheral soil are in contact, the boundary is intercepted to set reasonable constraint conditions, and the composite foundation calculation model is established.