Provided are a light-emitting device and a manufacturing method thereof, a display panel and a display device. The light-emitting device includes a plurality of light-emitting units including a first, a second, and a third light-emitting unit. Each light-emitting unit includes a micro-cavity structure including an anode, a hole transport layer, a functional layer, and a cathode. The functional layer of the first light-emitting unit includes a first light-emitting layer, a first buffer layer between the first light-emitting layer and the hole transport layer of the first light-emitting unit, and a second buffer layer between the first buffer layer and the first light-emitting layer. The material of the second buffer layer is different from that of the first buffer layer, the second buffer layer has a physical thickness less than or equal to 30 nanometers and an optical thickness less than or equal to 60 nanometers.