Abstract: This paper studies the expansion effects of strong magnetic field structure (SMFS) in interplanetary space (from 18 R_s to 240 R_s). Simulation results show that the main body of SMFSis typically with a strong magnetic field, low β, high μp, μk, low temperature and low density, but high temperature and density existing in the front and rear of the structure; expansion of SMFSresults in the saw-tooth profile of radial velocity; expansion velocity of SMFSobviously depends on the strength of magnetic field; there is almost no relation between propagation velocity of the structure center and the strength of magnetic field when SMFSis motionless relative to the inner boundary; the s ruoture can intensify (weaken) the compression to the plasma in the front (rear) of the structure when SMFSmoves relating to the inner boundary. The expansion of SMFScan generate a typical profile of magnetic cloud.