Abstract: In order to improve the output of LED light, a double-layer phosphor coating structure was designed based on the traditional phosphor coating. By studying the concentration of the upper-lower coating layer and the upper coating amount, the effect of the double-layer coating structure on the LED light output of the chips on board (COB) encapsulation was explored. The results show that when the current is 440 mA, a white light LED with a COB encapsulation structure of 15 W is finally realized in the experiment: 1) When only yellow phosphor is coated, the upper-lower rubber powder ratio is 14.2～28, and the volume of the upper coating layer is 0.8 times than that of the lower layer, the LED luminous flux of the COB encapsulation is 2 179 lm, the luminous efficiency can reach to 145.3 lm / W, the color rendering index is 63, and the maximum increase in light output is 7.82%. 2) The phosphor is adjusted to the combination of yellow-green phosphor and red phosphor, and the final color temperature, light efficiency and color rendering index are 4 854 K, 129.7 lm/W and 82.1, respectively. Therefore, the double-layer phosphor coating structure can improve the optical performance of the COB-encapsulated LED, which has certain application value for the actual production.