Herein, the K₃MoO₂F₅^.2H₂O:Mn⁴⁺ phosphor was synthesized by using low toxic NH₄HF₂ and HCl instead of highly toxic HF. The K₃MoO₂F₅^.2H₂O:Mn⁴⁺ phosphor has a blocky structure and exhibits sharp red emission at the range of 580 to 670 nm excited by the blue light at 470 nm. The fabricated WLED device at 20 mA current has low correlation color temperature (CCT = 3608 K) and high color rendering index (Ra = 90.1), which can significantly improve the electroluminescence performance of cold WLED devices. These results indicate that the K₃MoO₂F₅^.2H₂O:Mn⁴⁺ phosphor has potential application value in warm WLED excited by blue light chip.