There are numerous cable shaft in nuclear power plants which have complex structure. And the shaft has many openings in vertical or horizontal directions to connect with other areas of nuclear power plants. In case of fire, shaft may become the path of rapid development and spread of fire, and it is easy to form stereoscopic fire, resulting in serious hazard. At present, there is a lack of in-depth theoretical analysis and experiment data of cable burning in shaft fire in nuclear power plants in our country. The author and her team investigated the common structure characteristic of nuclear power plants at home and abroad and built a large-scale cable shaft experiment platform. And then based on different types of combustibles and different movement of fire sources (i.e., moving or fixed), a series of experiments were conducted for studying the inner vertical temperature distribution and the smoke spreading characteristic in the shaft. Experiments found that there is no stratification in the distribution of gas in the upward spreading cable fire experiments, which accords with the assumption of single-zone model. However, in experiments with fixed fire source, there is an obvious stratification of fire plume, hot gas layer and air in lower layer, which tells the single-zone model is no longer applicable. The results of the study could be used in optimizing the fire protection and safety analysis methods of shaft in nuclear power plants, and further improving the fire safety level of nuclear power plants.