  The binary YY Gem shows many interesting properties, one of which is the
periodicity in its flaring rate. The period, which is about $48 \pm 3$ min, was
ever interpreted in terms of the oscillation of a filament. In this paper, we
propose a new model to explain this phenomenon by means of 2.5-dimensional MHD
numerical simulations. It is found that magnetic reconnection is induced as the
coronal loops rooted on both stars inflate and approach each other, which is
driven by the differential stellar rotation. The magnetic reconnection is
modulated by fast-mode magnetoacoustic waves which are trapped between the
surfaces of the two stars, so that the reconnection rate presents a periodic
behaviour. With the typical parameters for the binary system, the observed
period can be reproduced. We also derive an empirical formula to relate the
period of the flaring rate to the coronal temperature and density, as well as
the magnetic field.
