The invention relates to a method for synthesising mesoporous tin oxide by three-dimensional mesoporous silicon dioxide hard template. The thermal stability of the mesoporous tin oxide synthesised by a soft template is poor. The invention comprises the following steps of using a silicon dioxide molecular sieve with a three-dimensional mesoporous structure as a hard template, using stannous chloride as a tin source, ultrasonically dispersing the stannous chloride in the pore canals of the molecular sieve, roasting, removing the template, and drying to obtain the mesoporous tin oxide. The method provided in the invention is simply and conveniently operated and has low cost. The prepared mesoporous tin oxide has high thermal stability and controllable structure and specific surface area.