  We study the effect of Landau-Zener (LZ) tunneling caused by the varying
sweeping rate of external field, formulating and approximately solving the
problem with many levels of the LZ tunneling rate. Comparing with the steadily
vary about sweeping field, the LZ tunneling rate will be essentially changed
because of the unsteady variation of the sweeping field in time. Thus could
help us to make the particles with in lower states transit periodically to
upper states within the finite time.
