  This paper reports the study of $D_s^+\to \tau^+\nu$ via
$\tau^+\to\pi^+\bar{\nu}_\tau$ using a boosted decision tree method, with
$7.33$ fb$^{-1}$ of $e^{+}e^{-}$ collision data collected by the BESIII
detector at center-of-mass energies between $4.128$ and $4.226$~GeV. The
branching fraction of $D_s^+\to \tau^+\nu_\tau$ is determined to be
$(5.44\pm0.17_{\rm stat}\pm0.13_{\rm syst})\%$. The product of the $D_s^+$
decay constant $f_{D_s^+}$ and the CKM matrix element $|V_{cs}|$ is
$f_{D_s^+}|V_{cs}| = (248.3\pm3.9_{\rm stat}\pm3.1_{\rm syst}\pm1.0_{\rm
input})~\mathrm{MeV}$. Combining with the $|V_{cs}|$ value obtained from the
Standard Model global fit or the $f_{D_s^+}$ from the lattice quantum
chromodynamics, we determine $|V_{cs}| = 0.993\pm0.015_{\rm stat}\pm0.012_{\rm
syst}\pm0.004_{\rm input}$ and $f_{D_s^+} = (255.0\pm4.0_{\rm stat}\pm3.2_{\rm
syst}\pm1.0_{\rm input})~\text{MeV}$. The first uncertainty is statistical, the
second one is systematic and the third one is due to the input parameters,
mainly the lifetime of $D_s^+$. All results obtained in this work supersede the
BESIII previous results based on 6.32 fb$^{-1}$ of $e^+e^-$ collision data
taken at center-of-mass energies between $4.178$ and $4.226$~GeV.
