  In this paper, the high-precision light curves of $Kepler$ target KIC 5950759
are analyzed. The Fourier analysis of the long cadence light curve reveals 3
independent frequencies. Two of them are main pulsation modes: F0 =
14.221373(21) $\rm{d^{-1}}$ and F1 = 18.337249(44) $\rm{d^{-1}}$. The third
independent frequency $f_m$ = 0.3193 d$^{-1}$ is found in long cadence data
with a signal-to-noise ratio of 6.2. A weak modulation of $f_m$ to F0 and F1
modes (triplet structures centred on F0 and F1) are detected both in long and
short cadence data. This is the first detection of the modulation effect in a
double-mode HADS star. The most possible cause of the modulation effect in the
light curves is amplitude modulation with the star's rotation frequency of
0.3193 d$^{-1}$. The preliminary analysis suggests that KIC 5950759 is in the
bottom of the HADS instability strip and likely situated in the main sequence.
Spectroscopic observations are necessary to verify the true nature of the
modulation terms.
