Currently, lead halide perovskite quantum dots (PeQDs) have attracted great attention due to their spectacular photophysical properties. However, the toxicity of Pb²⁺ heavy metal ions in CsPbX₃ PeQDs limits their practical applications. Herein, a facile post-treatment doping method is proposed, which enables the preparation of highly luminescent low-toxic CsPbX₃:Mn²⁺ PeQDs from nonluminescent Cs₄PbX₆ PeQDs at water interface. The monodispersed CsPbX₃:Mn²⁺ PeQDs exhibit excellent photophysical properties, including high photoluminescence quantum yield up to 87%. The reaction process and doping mechanism are deeply explored through in-situ monitoring. By simply adjusting the halide composition of the original Cs₄PbX₆ PeQDs or Mn doping concentration, a series of CsPbX₃:Mn²⁺ PeQDs with adjustable emission could be obtained. Further, the CsPbX₃:Mn²⁺ Q-LED was fabricated and exhibited excellent orange light with the color coordinates of (0.564, 0.399), correlated color temperature (CCT) of 1,918 K, and luminous efficiency (LE) of 24 lm/W, which illustrate the great promise in light emitting diode (LED) applications. This work not only provides a facile method for the preparation of highly luminescent low-toxic CsPbX₃:Mn²⁺ PeQDs, but also provides insights into the mechanism of doping process.