The DD33 superalloy with ultra-low nitrogen (N) content was prepared by vacuum induced melting, and the effect of N on micro-pores in the DD33 single crystal nickel-base superalloy during solidification and homogenization was investigated by in-situ X-ray computed tomography (XCT). Results indicate that the volume fraction of micro-pores, including shrinkage pores and gas pores, increases from 0.08% to 0.11% with increasing N content from 5 ppm to 45 ppm during solidification. Correspondingly, the level of micro-pores in the sample with high N content is higher than that in the sample with low N content during homogenization at 1,330 °C for different time periods. However, the evolution behaviors of gas pores is different from that of shrinkage pores during solidification and homogenization. The number of gas pores is obviously larger in the high N sample during solidification, while the number of shrinkage pores and gas pores is almost the same in both samples after 1 h homogenization. Quantitative results show that the annihilation of micro-pores is associated with bubble diffusion, while the growth behavior of micro-pores during further exposure is dominated by Kirkendall-Frenkel effect.