The invention provides an extranuclear parallel computing method for electromagnetic radiation and scattering of an electric large object, comprising the following steps of: blocking and parallelly storing an impedance matrix by adopting a hard disk storage instead of an internal storage; and carrying out extranuclear subblocking and solving on a matrix equation in an MPI (Multiple Point Interface) parallel environment. The invention not only solves the problem of insufficient memory, but also rapidly finishes solving the problem by using physical memories of various computing nodes to the maximum extent; by using the method, the electromagnetic radiation and the scattering characteristic of an electric large-size object in one or more computers can be computed, the aim of replacing the memory by a hard disk can be achieved and the problem of insufficient memory caused by large computing quantity can be solved; and the computing result obtained by the method is completely consistent with the computing result obtained by a conventional intranuclear parallel computing method without losing any computing precision.