The invention relates to a preparation method and system of aerogel powder. According to the method and the system, provided by the invention, a lot of waste acid in a production process is used for replacing reaction material acid to prepare phase change materials including a salt mixture or a crystallized hydrated salt and the like, so that the aim of changing the waste acid into valuable things is realized. Meanwhile, an organic solvent is also recycled in a production process, so that a process flow of silicon dioxide aerogel has no waste liquid discharging.