  Rapidly developing photonics brings many interesting resonant optical
phenomena, in which the Fano resonance (FR) always intrigues researchers
because of its applications in optical switching and sensing. However, its
sensitive dependence on environmental conditions makes it hard to implement in
experiments. We in this work suggest a topologically-protected FR based on the
photonic valley Hall insulators, immune to the system impurities. The
topologically-protected FR is achieved by coupling the valley-dependent
topological edge states (TESs) with one double-degenerate cavity. The
$\delta$-type photonic transport theory we build reveals that this topological
FR dates from the interference of the two transmissions that are attributed to
the parity-odd cavity mode and the parity-even one. We confirm that the induced
Fano line shape of the transmission spectra is robust against the bending
domain walls and disorders. Our work may provoke exciting frontiers for
manipulating the valley transport and pave a way for the topologically
protected photonic devices such as optical switches, low-threshold lasers, and
ultra-sensitive sensors.
