All-inorganic perovskite CsPbX3 (X=Cl, Br and I) quantum dots (QDs) have been wildly utilized in optoelectronic devices due to its tunable photoluminescence, high photoluminescence quantum yield (PLQY), and narrow-line width photoluminescence. However, the blue luminescence PLQY of CsPbX3 perovskite quantum dots is still lag behind their red and green luminescence (PLQYs nearly 100%) counterparts. Herein, we present a facile strategy to synthetic ultra-small blue luminescence Sn2%2B ions doped CsPbBr3 perovskite QDs by supersaturated recrystallization synthetic approach at room temperature, and the particle size of as-prepared QDs is lower than 4 nm. The crystal structure, morphology, optical property, and stable luminescence property of Sn2%2B doped CsPbBr3 QDs are characterized by XRD, TEM, ultraviolet-visible spectrophotometer, and fluorescence spectrophotometer. The results show that the particle size of as-prepared QDs is slightly shrink from 3.33 nm (SnBr2 0.03 mmol) to 2.23 nm (SnBr2 0.06 mmol) as the SnBr2 adding amount increase, but there is no obvious change in the lattice spacing of doped QDs. The partial Pb2%2B for Sn2%2B replacement leads to a blue-shift from 490 nm (SnBr2 0.03 mmol) to 472 nm (SnBr2 0.06 mmol) of the optical spectra. The highest PLQY and the strongest XRD diffraction of ultra-small Sn2%2B doped CsPbBr3 blue luminescence QDs is obtained by adding SnBr2 0.05 mmol, and the blue luminescence located at 472 nm with the PLQY of 53.4%. There is no any change in PL peak of Sn2%2B doped CsPbBr3 QDs (SnBr2 0.05 mmol) by storing it under the ambient atmosphere for 15 days, and the PLQY of Sn2%2B doped QDs is still remain 80% of the initial after 15 days. It is concluded that the crystallization and optical property could be effectively improved in Sn2%2B doped CsPbBr3 QDs by partially replacing appropriate amount of Pb2%2B ion by Sn2%2B ion. This ultra-small Tin doped CsPbBr3 blue luminescence QDs shows promising application in lighting-emitting diode and laser.