  Pulsar death line can be defined in $P-\dot{P}$ diagram. Traditionally,
radio-loud pulsars are supposed to locate above the death line where is the
radio-loud region. With the development of observational equipment, the
observational properties of the neutron star are remarkably diverse. In
$P-\dot{P}$ diagram, some of the special sources are radio-quiet but lie above
the death line. From the definition of the pulsar death line, different
equation of states for neutron star or strange star results in different death
lines. We discuss the influence of the equation of state on the pulsar death
line and the possible link between different neutron star groups. The results
show that central compact objects would be the small mass of self-bound strange
stars, and rotating radio transients might be old pulsars on the verge of
death. We suggest that PSR J2144-3933 is likely to be a large mass pulsar,
which would be larger than $2.0\rm{M_{\odot}}$. Multiple observational facts
would help us to reveal the nature of pulsars.
