Abstract: A four-wire light string includes a first interface, a second interface, a plurality of LED lights connected between the first and second interfaces, a first conductive wire and a second conductive wire that are directly connected to the first and second interfaces, a plurality of third conductive wires each connected to a positive pole of the LED light, and a plurality of fourth conductive wires each connected to a negative pole of the LED light. Each four-wire light string constitutes a basic unit. When no additional basic unit is adopted, a current does not flow through the first conductive wire and the second conductive wire, but is directly connected to positive and negative poles of a power supply. Each basic unit has a small heating loss on the conductive wire, and adding more basic units will not cause a voltage drop, so that the light strings have basically the same brightness.