We established a method on measuring the $dzdzb$ mixing parameter $y$ for BESIII experiment at the BEPCII $e^+e^-$ collider. In this method, the doubly tagged $psi(3770) to D^0 overline{D^0}$ events, with one $D$ decays to CP-eigenstates and the othe
r $D$ decays semileptonically, are used to reconstruct the signals. Since this analysis requires good $e/pi$ separation, a likelihood approach, which combines the $dE/dx$, time of flight and the electromagnetic shower detectors information, is used for particle identification. We estimate the sensitivity of the measurement of $y$ to be 0.007 based on a $20fb^{-1}$ fully simulated MC sample.
