Abstract: In this paper, the feasibility of the improvement on the γ-ray sensitivity of current-mode CZT detector by subbandgap illumination was investigated. The effect of sub-bandgap illumination on the γ-ray sensitivity of CZT detector was analyzed by 60Co source instrument. The results show that under stable γray irradiation, the sharp peak in the output currentversus time curve (calibrated current curve) of CZT γray detector was mainly related to the detrapping effects of the deep level defect in CZT crystal. Illuminated by subbandgap light, the occupation of the deep level defect can be regulated. The sharp peak in the calibrated current curve can be eliminated and the performance of CZT detector can also be improved. When the photogenerated current induced by subbandgap illumination (850 nm) in CZT detector is 33.0 nA and the operated voltage is 200 V, the sensitivity of CZT detector to 1.25 MeV γray is 9.99×10-17 C·cm2. This experimental sensitivity is close to the simulated sensitivity of 1.18×10-16 C·cm2.