In this paper, video block-matching and 3D filtering (VBM3D) denoising has been proposed and experimentally demonstrated for the first time in 100.8 km long-distance Brillouin optical time domain analyzer (BOTDA) sensing system with 2 m spatial resolution. Both experiments under static and slowly varying temperature environment are carried out. A temperature uncertainty of 0.43°C has been achieved with denoising by VBM3D in static temperature measurement. To our knowledge, this is one of the best temperature uncertainty reported for a sensing distance beyond 100 km. The slowly varying temperature at the end of 100.8 km fiber has also been accurately measured. VBM3D exploits both the spatial and temporal correlations of the data for denoising, thus it can significantly reduce the temperature fluctuations and keep the measured values close to the real temperature even if the temperature is temporally changing. We believe it would be useful for the long-distance sensing where the measurand may have temporal evolution in the slowly varying environment.