  We attempt to apply the Regge trajectory approach to the heavy-light diquarks
composed of one heavy quark and one light quark. However, we find that the
direct application of the usual Regge trajectory formula for the heavy-light
mesons and baryons fails. In order to correctly estimate the masses of the
heavy-light diquarks, it is needed to consider the light quark mass correction
and the parameter $C$ in the Cornell potential within the Regge trajectory
formula. By using the modified Regge trajectory formulas, we are able to
estimate the masses of the heavy-light diquarks $(cu)$, $(cs)$, $(bu)$ and
$(bs)$, which agree with other theoretical results. It is illustrated that the
heavy-light diquarks satisfy the universal descriptions irrespective of heavy
quark flavors, similar to other heavy-light systems such as the heavy-light
mesons, the heavy-light baryons composed of one heavy quark (diquark) and one
light diquark (quark), and the heavy-light tetraquarks composed of one heavy
diquark (antidiquark) and one light antidiquark (diquark). The diquark Regge
trajectory provides a new and very simple approach for estimating the spectra
of the heavy-light diquarks.
