Abstract: Radar cross section（RCS） calculation of electrically large target using method of momen costs huge computer resource. The adaptive cross approximation (ACA)algorithm was applied to reduce the computation complexity and storage. Combined with the out-of-core solve technology, the above algorithm was paralleled to reduce hardware cost of large computation and improve compute speed further. Through a numerical example, it proves that the memory and compute time is reduced by this algorithm without losing the accuracy of metnd of moment MoM.