A phosphor device of an illumination system, which emits a first waveband light, includes a substrate and a first phosphor layer. The first phosphor layer includes a first phosphor agent and a second phosphor agent. The first phosphor agent is formed on the substrate for converting the first waveband light into a second waveband light. The second waveband light comprises a first color light and a second color light. The second phosphor agent is distributed over the first phosphor agent for converting the first waveband light into the second color light so as to increase the luminous intensity of the second color light. Therefore, the luminous intensity of the second color light can be effectively increased.