The invention discloses tin doped ferric oxide mesocrystal nano particles. The tin doped ferric oxide mesocrystal nano particles are formed by doping tin in ferric oxide mesocrystal nano particles formed through orientation stacking of ferric oxide nano particle crystals of 2 nm to 6 nm, the size of the tin doped ferric oxide mesocrystal nano particles ranges from 40 nm to 220 nm, and the specific surface area of the tin doped ferric oxide mesocrystal nano particles is 36.2 m<2>/g, wherein the molar weight of doped tin accounts for 0.01%-15% that of iron. A preparation method of the tin doped ferric oxide mesocrystal nano particles comprises the steps that 1, the ferric oxide mesocrystal nano particles are synthesized; 2, a proper quantity of ferric oxide mesocrystal nano particles and a tin source alcoholic solution in a corresponding proportion are mixed, stirring and volatilizing are carried out, and vacuum drying is carried out after volatilizing is completed; 3, the dried composite is placed in a muffle furnace to be calcined for 3 hours or longer at the temperature of 500 DEG C to 650 DEG C. The obtained tin doped ferric oxide mesocrystal nano particles have enhanced pollutant visible light catalytic degradation and photoelectrochemical water decomposition performance and can be commercially applied in the fields of pollutant photocatalytic degradation, photocatalytic water splitting hydrogen production, supercapacitors, lithium ion batteries and the like.