Poor water stability is the main problem of commercialized Mn4+-doped fluorides for white light emitting diode (LED) application. This work proposes a surface engineering strategy to rebuild a Mn-free fluoride shell on the fluoride to effectively resist the destruction of water molecules. By simple processing using glyoxylic acid (GA) solution, the moisture resistance of the red-emitting fluorides can be significantly improved. The photoluminescence (PL) quantum efficiency (QE) the surface-engineered K2SiF6:Mn4+ (KSFM-GA) still maintain 98.43% after water immersion for 360 h, in sharp contrary to the untreated one (PLQE decreased to 59.79%). Additionally, PL intensity of hydrolysed KSFM can recover to 99.1% by treatment of the reducing GA solution. By using the high-stability KSFM-GA red phosphor, the as-fabricated high-performance warm-white-LED device can still maintain 84.6% in luminous efficacy, higher than that (79.6%) with untreated KSFM, after 500 hours of aging in a high temperature (85 oC) and high humidity (85%) environment.