Embodiments of the disclosure provide an Organic Light-Emitting Diode (OLED) display device and an encapsulation method thereof. The encapsulation method of the OLED display device comprises: providing a display substrate, the display substrate having a display region and a peripheral region provided outside the display region; forming a dam in the peripheral region of the display substrate; and forming a plurality of thin film encapsulation layers on the display substrate by using a single mask plate, wherein the plurality of thin film encapsulation layers envelop the dam therein.