  A new self-sustained model for long-term light curve variations of RX
J0513.9-6951 is proposed based on an optically thick wind model of
mass-accreting white dwarfs (WDs). When the mass accretion rate to a WD exceeds
the critical rate of \sim 1 x 10^{-6} M_\sun yr^{-1}, optically thick strong
winds begin to blow from the WD so that a formation of common envelope is
avoided. The WD can accrete and burn hydrogen-rich matter atop the WD at the
critical rate. The excess matter transferred to the WD above the critical rate
is expelled by winds. This is called the accretion wind evolution. This
ejection process, however, occurs intermittently because the mass transfer is
attenuated by strong winds: the strong winds collide with the secondary surface
and strip off the very surface layer of the secondary. The matter stripped-off
is lost from the binary system. Properly formulating this mass stripping effect
and the ensuing decay of mass transfer rate, we are able to reproduce, in a
self-sustained manner, the transition between the optical high/X-ray off and
optical low/X-ray on states of RX J0513.9-6951. Thus RX J0513.9-6951 is the
first example of the accretion wind evolution, which is a key evolutionary
process in a recently developed evolutionary path to Type Ia supernovae.
