LED (Light Emitting Diode) is widely used in lighting, display, backlight and many other fields because of its energy saving, environmental protection, long life, low voltage and short switching time. At present, it is developing in the direction of higher brightness, high color, high weather resistance and high luminous uniformity. The LED industry chain can be divided into upper, middle and lower reaches, which are LED epitaxy chips, LED packaging and LED applications. As a link between the top and bottom of the LED industry chain, LED packaging plays an important role in the whole industry chain. LED is composed of chips, wires, brackets, conductive adhesives and packaging materials, among which packaging materials are one of the key factors affecting the performance and service life of LED. At present, because of its special requirements for transparency, packaging materials are mainly used in the market, such as epoxy resin, silicone, polycarbonate, glass, polymethacrylate and other high transparency materials. However, most of these materials are harder and inconvenient to process, so they are basically used for outer lens materials. Traditional LED epoxy resin packaging materials have some defects, such as high internal stress, poor heat resistance and easy aging, which can not meet the growing demand of the performance of LED packaging materials. They are gradually replaced by silicone materials or silicone modified materials. Silicone material is a kind of material with high ultraviolet resistance, high aging resistance and low stress. It has become an ideal choice for LED packaging materials. The transmittance of silicone resin is proportional to the luminous intensity and efficiency of LED devices. The higher the transmittance, the better the luminous intensity and efficiency of LED devices. Because GaN chips have high refractive index (about 2.2), the refractive index of ordinary silicone materials is only 1.4. Therefore, improving the refractive index of silicone materials can reduce the difference between the refractive index of silicone chips, reduce the light loss caused by interface reflection and refraction, and enhance the light extraction efficiency of LED devices.