The authors had proposed a new detection method for partial discharge (PD) occurring in sulfur hexafluoride (SF6) gas using a carbon nanotube (CNT) gas sensor. In the previous study, we had investigated the dependency of gas sensor response on applied voltage and gas sensor position. In this paper, a series of experiments was performed to observe dynamic behavior of decomposition gas using the CNT gas sensor. The gas sensor responses to PD under several SF6 gas pressures were measured. It was found that the sensor response normalized by PD power increased almost linearly with the gas pressure. The result is useful to understand the mechanism how the gas pressure influences the generation and diffusion of decomposition gas. Effects of absorbent placed inside the discharge chamber were also investigated. Finally, the gas sensor responses were measured with a time interval after PD was extinguished to check if an offline diagnosis was possible. Although the sensor response decreased with elapsed time after PD was extinguished, it was still possible to detect the residual decomposition gas using the CNT gas sensor.