Based on method M, a method of calculating the displacement of large-diameter and ultra-long pile group in soft soil is put forward. Analysis on single pile, cushion cap and pile group are associated by this new method. The turn angle of the cap, effective pile length, and the pile group compression and bending induced by horizontal force  rotation are also taken into account by this method. A computer program for the method is developed in Matlab. The results of various factors, such as pile space and pile diameter, are discussed. The calculated values are substituted back in the single pile equation generated by method M to obtain the pile displacement curve and pile stress curve. The method is a closed cycling process. It is applied to the analysis on actual data of anchorage foundation pile group of a bridge crossing Yangtze River in Anhui Province. It is found by comparing the calculation results with results from finite difference method that the method is of high practical value.