  Based on first-principles calculations and symmetry analysis, we report that
the three-dimensional (3D) nodal line (NL) semimetal phases can be realized in
the lead dioxide family (\emph{$\alpha$}-PbO$_2$ and \emph{$\beta$}-PbO$_2$)
and its derivatives. The \emph{$\beta$}-PbO$_2$ features two orthogonal nodal
rings around the Fermi level, protected by the mirror reflection symmetry. The
effective model is developed and the related parameters are given by fitting
with the HSE06 band structures. The NLs mainly come from the $p$ orbitals of
the light element O and are rather robust against such tiny spin-orbit
coupling. The NL phase of the \emph{$\alpha$}-PbO$_2$ can be effectively
tailored by strain, making a topological phase transition between a
semiconductor phase and a NL phase. In addition, the exploration of
\emph{$\beta$}-PbO$_2$ derivatives (i.e. \emph{$\beta$}-PbS$_2$ and
\emph{$\beta$}-PbSe$_2$) and confirmation of their topological semimetallicity
greatly enrich the NL semimetal family. These findings pave a route for
designing topological NL semimetals and spintronic devices based on realistic
PbO$_2$ family.
