  Entanglement-based quantum key distribution (QKD) is an essential ingredient
in quantum communication, owing to the property of source-independent security
and the potential on constructing large-scale quantum communication networks.
However, implementation of entanglement-based QKD over long-distance optical
fiber links is still challenging, especially over deployed fibers. In this
work, we report an experimental QKD using energy-time entangled photon pairs
that transmit over optical fibers of 242 km (including a section of 19 km
deployed fibers). High-quality entanglement distribution is verified by
Franson-type interference with raw fringe visibilities of 94.1$\pm$1.9% and
%92.4$\pm$5.4% in two non-orthogonal bases. The QKD is realized through the
protocol of dispersive-optics QKD. A high-dimensional encoding is applied to
utilize coincidence counts more efficiently. Using reliable, high-accuracy time
synchronization technology, the system operates continuously for more than 7
days, even without active polarization or phase calibration. We ultimately
generate secure keys with secure key rates of 0.22 bps and 0.06 bps in
asymptotic and finite-size regime,respectively. This system is compatible with
existing telecommunication infrastructures, showing great potential on
realizing large-scale quantum communication networks in future.
