  We study the properties of the upper critical field of superconductivity in
nodal-line semimetals in a continuous model, which has a nodal-line on the
$k_{z} = 0$ plane. Using the semiclassical Green's function method, we
calculate the upper critical field for the two limiting cases: the dirty limit
with many impurities and the clean limit with few impurities. The results show
the large anisotropy of the magnitude of the upper critical field and the
unusual temperature dependence. The obtained results are compared with recent
experimental data of PbTaSe$_{2}$.
