  The clarity of nights is the major factor that should be carefully considered
for optical/infrared astronomical observatories in site-testing campaigns.
Cloud coverage is directly related to the amount of time available for
scientific observations at observatories. In this article, we report on the
results of detailed night-time cloud statistics and continuous observing me
derived from ground-based all-sky cameras at the Muztagh-ata site from 2017 to
2021. Results obtained from acquisition data show that the proportion of the
annual observing me at the Muztagh-ata site is 65%, and the best period with
the least cloud coverage and longer continuous observing time is from September
to February. We made a comparison of the monthly mean observing nights obtained
from our all-sky cameras and CLARA dataset, results show that the discrepancy
between them may depend on the cloud top heights. On average, this site can
provide 175 clear nights and 169 nights with at least 4 hours of continuous
observing time per year.
