  In this paper, we present an analysis of the pulsating behavior of $Kepler$
target KIC 10284901. The Fourier transform of the high-precision light curve
reveals seven independent frequencies for its light variations. Among them, the
first two frequencies are main pulsation modes: F0 = 18.994054(1)
$\rm{day^{-1}}$ and F1 = 24.335804(4) $\rm{day^{-1}}$, the ratio of F0/F1 =
0.7805 classifies this star as a double-mode high-amplitude $\delta$ Scuti
(HADS) star; another two frequencies, $f_{m1}$ = 0.4407 day$^{-1}$ and $f_{m2}$
= 0.8125 day$^{-1}$, are detected directly, and the modulations of $f_{m1}$ and
$f_{m2}$ to F0 and F1 modes (seen as quintuplet structures centered on these
two modes in the frequency spectrum) are also found. This is the first
detection of a double-modulation effect in the HADS stars. The features of the
frequency pattern and the ratio ($f_{m1}$/$f_{m2}$ $\approx$ 1:2), as well as
the cyclic variation of amplitude of the two dominant pulsation modes, which
seem to be similar to that in Blazhko RR Lyrae stars, indicate this modulation
might be related to the Blazhko effect. A preliminary analysis suggests that
KIC 10284901 is in the bottom of the HADS instability strip and situated in the
main sequence.
