A white-light emitting device and its preparation method are provided. The white-light emitting device comprises an ultraviolet (UV) light emitting diode (LED) chip, a first phosphor, and a second phosphor, wherein the UV LED chip generates a first radiation; the first phosphor is composed of Zn(C3N2H4)2 powder and is excited by the first radiation to generate a second radiation; and the second phosphor is excited by the first radiation and/or the second radiation to generate a third radiation. The third radiation is then mixed with the first radiation and/or the second radiation to generate a white light.