  In this paper, I report the preliminary results of the strong phase
difference $\cos\delta_{K\pi}$ between the doubly Cabibbo-suppressed process
$\overline{D}{}^0\to K^- \pi^+$ and Cabibbo-favored $D^0\to K^- \pi^+$ at
BESIII. In addition, the preliminary results of the $D^0$-$\overline{D}{}^0$
mixing parameter $y_\mathrm{CP}$ by analyzing $CP$-tagged semileptonic $D$
decays are presented. These measurements were carried out based on the
quantum-correlated technique in studying the process of $D^0\overline{D}{}^0$
pair productions of 2.92 fb$^{-1}$ $e^+e^-$ collision data collected with the
BESIII detector at $\sqrt{s}$ = 3.773 GeV.
