All inorganic colloid CsPbX₃ (X = Cl,Br,I) perovskite quantum dots (PeQDs) have become a promising new optoelectric material due to their excellent optical properties. However, the implementation of strong quantum constraints in PeQDs still faces great challenges, and there is still a lack of reliable methods to accurately control the PeQD size and luminescence performance. Here, ultra-small-size and highly luminous CsPbBr₃ PeQDs have been prepared by hot injection method with a novel synthesis strategy. A cesium and ligand combined compound of cesium-dodecyl benzene sulfonic acid (Cs-DBSA) is employed as Cs and ligand sources concurrently. The ultra-small-size of CsPbBr₃ PeQDs can be effectually controlled by the Cs-DBSA solution concentration. In particular, the synthesis route we developed can be terminated within 15 s after hot injection processing, which is rather different from previously reported methods including mechanical grinding, low temperature, and great Br/Pb ratio methods. Typical colloidal PeQDs show excellent comprehensive performance that having a minimum size up to 1.8 nm, unimodal photoluminescence (PL) with peak at 448.8 nm, high photoluminescence quantum yield (PLQY) up to 100%, and good light and color stabilities. As a healthy light source, spectral intensity uniformly distributed white-light-emitting diodes (WLED) have been realized by using the CsPbBr₃ PeQDs to increase components of cyan light. The above results show that our proposed synthesis strategy is simple, rapid and effective, which is a significant step forward in the field of small-size PeQDs, and helpful for realizing large-scale industrial production of PeQDs.