  We have collected the parameter of 38 neutron stars (NSs) in binary systems
with spin periods and measured masses. By adopting the Boot-strap method, we
reproduced the procedure of mass calculated for each system separately, to
determine the truly mass distribution of the NS that obtained from observation.
We also applied the Monte-Carlo simulation and introduce the characteristic
spin period 20 ms, in order to distinguish between millisecond pulsars (MSPs)
and less recycled pulsars. The mass distributions of MSPs and the less recycled
pulsars could be fitted by a Gaussian function as $\rm 1.45\pm0.42 M_{\odot}$
and $\rm 1.31\pm0.17 M_{\odot} (\rm with ~ 1\sigma)$ respectively. As such, the
MSP masses are heavier than those in less recycled systems by factor of $\rm
\sim 0.13M_{\odot}$, since the accretion effect during the recycling process.

High Energy Astrophysical Phenomena