  So far, in total 15 double neutron star systems (DNSs) with a reliable
measurement of the total gravitational mass ($M_{\rm T}$) have been detected in
the Galaxy. In this work we study the distribution of $M_{\rm T}$. The data
prefer the double Gaussian distribution over a single Gaussian distribution and
the low and high mass populations center at $M_{\rm T}\sim 2.58M_\odot$ and
$\sim 2.72M_\odot$, respectively. The progenitor stars of GW170817 have a
$M_{\rm T}=2.74^{+0.04}_{-0.01}M_\odot$, falling into the high mass population.
With a local neutron star merger rate of $\sim 10^{3}~{\rm Gpc^{-3}~yr^{-1}}$,
supposing the $M_{\rm T}$ of those merging neutron stars also follow the double
Gaussian distribution, the upcoming runs of the advanced LIGO/Virgo will soon
detect some events with a $M_{\rm T}\lesssim 2.6M_\odot$ that can effectively
probe the equation of state of the neutron stars and the distribution function
is expected to be reliably reconstructed in the next decade.
