  With the help of Gaia data, it is noted that in addition to the core
components, there are low-density outer halo components in the extended region
of open clusters. To study the extended structure beyond the core radius of the
cluster ($\sim$ 10 pc), based on Gaia EDR3 data, taking up to 50 pc as the
searching radius, we use the pyUPMASK algorithm to re-determine the member
stars of the open cluster within 1-2 kpc. We obtain the member stars of 256
open clusters, especially those located in the outer halo region of open
clusters. Furthermore, we find that most open clusters' radial density profile
in the outer region deviates from the King's profile. To better describe the
internal and external structural characteristics of open clusters, we propose a
double components model for description: core components with King model
distribution and outer halo components with logarithmic Gaussian distribution,
and then suggest using four radii ( $r_c$, $r_t$, $r_o$, $r_e$) for describing
the structure and distribution profile of star clusters, where $r_t$ and $r_e$
represent the boundaries of core components and outer halo components
respectively. Finally, we provide a catalog of 256 clusters with structural
parameters. In addition, our study shows the sizes of these radii are
statistically linear related, which indicates that the inner and outer regions
of the cluster are interrelated and follow similar evolutionary processes.
Further, we show that the structure of two components can be used to better
trace the cluster evolution properties in different stages.
