The X-ray radiation response and radiation damage of CdZnTe (CZT) detector were studied in this paper. After rapid temperature annealing, the linearity of I-V curve was much better than before. Photo current of Au/CZT planar detector increased linearly with the X-ray intensity. An inflection point around 10-30 V was observed for different X-ray intensity. Below the inflection points, with the increase of applied voltage, photon current increased linearly, while the current still increased after the inflection point likely due to the illumination-related impact ionization effect. In addition, under exposure in strong X-ray intensity, the photo current remains unchanged before the inflection point while it changes significantly with after the inflection point.