  Optical clock networks play important roles in various fields, such as
precise navigation, redefinition of "second" unit, and gravitational tests. To
establish a global-scale optical clock network, it is essential to disseminate
time and frequency with a stability of $10^{-19}$ over a long-distance
free-space link. However, such attempts were limited to dozens of kilometers in
mirror-folded configuration. Here, we take a crucial step toward future
satellite-based time-frequency disseminations. By developing the key
technologies, including high-power frequency combs, high-stability and
high-efficiency optical transceiver systems, and efficient linear optical
sampling, we demonstrate free-space time-frequency dissemination over two
independent links with femtosecond time deviation, $3\times10^{-19}$ at 10,000
s residual instability and $1.6\times10^{-20}\pm 4.3\times10^{-19}$ offset.
This level of the stability retains for an increased channel loss up to 89 dB.
Our work can not only be directly used in ground-based application, but also
firmly laid the groundwork for future satellite time-frequency dissemination.
