  We study the radiation damping effect on the relativistic acceleration of
electron-positron plasmas with two-and-half-dimensional particle-in-cell (PIC)
simulation. Particles are accelerated by Poynting flux via the diamagnetic
relativistic pulse accelerator (DRPA), and decelerated by the self-consistently
solved radiation damping force. With $\Omega_{ce}/\omega_{pe}\geq 10$, the
Lorentz factor of the highest energy particles reaches gamma>100, and the
acceleration still continues. The emitted radiation is peaked within few
degrees from the direction of Poynting flux and strongly linearly polarized,
which may be detectable in gamma-ray burst(GRB) observations. We also show that
the DRPA is insensitive to the initial supporting currents.
