A large and reversible upconversion (UC) luminescence modulation has been found in the Na0.498Bi0.498TiO3:0.002Er (NBT:0.002Er) based on the photochromic reaction. The dependence of luminescence modulation of the ceramics on the wavelength of irradiation light and sintering temperature was investigated. It was found that the optimized sintering temperature and irradiation wavelength were 1130 degrees C and 405 nm, respectively. The highest Delta R-t (defined as: Delta R-t = (R-0 - R-t)/R(0)x100(%), where R-0 and R-t are the initial emission intensity and that after different irradiation time, respectively) value of 44.9% was obtained for the ceramics sintered at 1130 degrees C after irradiation at 405nm. More importantly, for the poled ceramics, Delta R-t value was promoted to a high value of 75.5%, which was 168% of that of the unpoled ones. The mechanism of luminescence modulation and its enhancement via electric field poling were discussed. This study demonstrated that electric field poling was an effective strategy to enhance the PC reaction in the NBT ceramics.