Abstract: By using the Ritz vector direct superposion method for dynamic ana-lysis usually is average ten times faster than subspace iteration method, The procedure of Ritz vector method is mainly a series of static solving, Therefore the blocked out-of-core solver has applied quite efficiently to solve the natural frequenies and mode shapes of large structure in this pap-er and the in-core memory requirement was reduced greatly,Three program segments are set in SAP81 and run on microcomputer with critical in-core memory.The capacity of the dynamic analysis of SAP81 has arised about four times larger than before.