Due to the low color rendering of high-power white light-emitting diodes (LEDs) based on yttrium aluminum garnet-based (YAG) yellow phosphors, high color-rendering white LEDs by mixing multiple-phosphors have been accepted by LED industry. However, the difference of phosphors can result in the luminous-chromatic-thermal stability and reliability problems in LED packages. This study selects yellow, red and orange phosphors used in high color rendering white packages, analyzes their luminescence and thermal properties, crystal structures and micro morphologies during both the high temperature and high moisture ageing test and the water-soaking test, and finally figures out the degradation mechanisms of different phosphors. The results show that: 1) the hydrolysis reaction of phosphors under hygrothermal environment produces OH- and increases the environment’s pH, that can lower the crystallinity of phosphor hosts, increase the lattice vibration and light-induced heat, and enhance the thermal quenching effect of phosphors. Meanwhile, the surface roughening of phosphor particles can increase the blue light scattering and lower its absorption and conversion efficiency. 2) the degradation trends of both luminescence and thermal properties of phosphors under the water-soaking test are similar to those aged under high temperature and high moisture ageing test. So it is an effective method to assess the reliability of LED phosphors under hygrothermal environment.