  Using $e^+e^-$ collision data collected with the BESIII detector at seven
energy points ranging from 3.68 to 3.71 GeV and corresponding to an integrated
luminosity of $652.1~{\rm pb^{-1}}$, we present an energy-dependent measurement
of the transverse polarization, relative phase and modulus ratio of the
electromagnetic form factors of the $\Sigma^+$ hyperon in the $e^+e^- \to
\Sigma^+ \bar{\Sigma}^-$ reaction. These results are helpful to understand the
production mechanism of the $\Sigma^+$-$\bar\Sigma^-$ pairs.
