The photoluminescence quantum yields (PLQYs) of all-inorganic halide perovskites in the green and red spectral ranges have approached over 90%, overwhelmingly arousing burgeoning interests for creating a revolution in next-generation high-definition displays. However, obtaining pure blue-emitting perovskites with high PLQYs still remains a challenge. Herein, we designed a novel strategy to pre-optimize CsPbCl3 quantum dots (QDs) using praseodymium(iii) chloride (PrCl3), and then efficient blue-emitting CsPbBrxCl3-x QDs were obtained through halide exchange between the optimized CsPbCl3 and efficient CsPbBr3 QDs. Specifically, the PrCl3 optimization simultaneously and efficiently passivated the surface vacancy defects and appropriately reduced the surface long-chain organic ligands of the CsPbCl3 QDs, synergistically eliminating the deep trap states, and hence considerably suppressing nonradiative recombination. As a result, the radiative recombination rate was enhanced by more than one order of magnitude from 4.3 to 79 μs-1. Benefiting from this, the blue-emitting CsPbBrxCl3-x QDs exhibited an admirable PLQY of up to 89%, which is competitive compared with that of the state-of-the-art red and green-emitting perovskites. This strategy provides a unique understanding regarding the low PLQY of blue-emitting perovskites and an efficient method to boost it, which is especially attractive for constructing efficient blue and white light-emitting diodes.