  Circular-ribbon flares (CFs) are a special type of solar flares owing to
their particular magnetic topology. In this paper, we conducted a comprehensive
statistical analysis of 134 CFs from 2011 September to 2017 June, including
four B-class, 82 C-class, 40 M-class, and eight X-class flares, respectively.
The flares were observed by the Atmospheric Imaging Assembly (AIA) on board the
Solar Dynamics Observatory (SDO) spacecraft. The physical properties of CFs are
derived, including the location, area ($A_{CF}$), equivalent radius ($r_{CF}$)
assuming a semi-spherical fan dome, lifetime ($\tau_{CF}$), and peak SXR flux
in 1$-$8 {\AA}. It is found that all CFs are located in active regions, with
the latitudes between -30$^\circ$ and 30$^\circ$. The distributions of areas
and lifetimes could be fitted with a log-normal function. There is a positive
correlation between the lifetime and area. The peak SXR flux in 1$-$8 {\AA} is
well in accord with a power-law distribution with an index of $-$1.42. For the
134 CFs, 57\% of them are accompanied by remote brightenings or ribbons. A
positive correlation exists between the total length ($L_{RB}$) and average
distance ($D_{RB}$) of remote brightenings. About 47\% and 51\% of the 134 CFs
are related to type III radio bursts and jets, respectively. The association
rates are independent of flare energies. About 38\% of CFs are related to
mini-filament eruptions, and the association rates increase with flare classes.
Only 28\% of CFs are related to CMEs, meaning that a majority of them are
confined rather than eruptive events. There is a positive correlation between
the CME speed and peak SXR flux in 1$-$8 {\AA}, and faster CMEs tend to be
wider.
