A light emitting diode (LED) lighting device and assembly method thereof. The LED lighting device includes: a base having a mounting surface; an LED element disposed on the mounting surface of the base; a lens component disposed at a side of the mounting surface of the base; a gasket disposed between the base and the lens component, such that the LED element is located within an area surrounded by the gasket; a fastener comprising a first portion and a second portion, wherein the first component is disposed at the side of the lens component opposite to the base and facing a portion of the lens component, the second portion extends from the first portion and is connected to the base, and the first portion of the fastener applies a pressure on the lens component towards the base.