The radiation transport effect on pellet implosion and the Rayleigh-Taylor (R-T) instability are studied in a light-ion beam (LIB) inertial confinement fusion (ICF) by numerical simulation and analytic work. First, we present the nonuniformity-smoothing effect of the radiation transport on implosion symmetry in an LIB ICF fuel pellet. The 2-D implosion simulation shows that the initial nonuniformity can be smoothed out well in an LIB ICF pellet; for example, the initial nonuniformity of 6% is smoothed to 0.07% during the implosion phase. In addition, linear analyses for the R-T instability under nonuniform acceleration in space and under radiation are also performed: The nonuniform acceleration field in space does not change the growth rate (γ) of the R-T instability. However, this nonuniformity may suppress the growth itself of the R-T instability. Radiation may reduc the growth rate (γ).