An electronic transformer-controlled LED lamp system comprising a control box and a two-wire LED lamp string, wherein a plug is arranged on the control box, an electronic controller is arranged in the control box, and two wires are output from the electronic controller and connected with said LED lamp string; the electronic controller comprises an alternating-current power supply, a full-bridge rectification circuit, a filter circuit, a step-down output circuit and an output function control circuit, wherein the step-down output circuit comprises a first single chip and a transformer, a first pin of the first single chip is connected with a circuit ground, a second pin of the first single chip is connected with one end of a first resistor and an emitter of a first triode, a third pin of the first single chip is connected with the base of the first triode, a fifth pin of the first single chip is connected with one end of a first capacitor, and a sixth pin of the first single chip is connected with the positive pole of a second capacitor; the negative pole of the second capacitor is connected with the circuit ground; and a cathode of a first diode is connected with the positive pole of the second capacitor; the other end of the first resistor is connected with the circuit ground; one end of a second resistor is connected with the positive pole of the second capacitor, an anode of a second diode is connected with one end of a primary coil of the transformer, a first end of a second secondary coil of the transformer is connected with an anode of said first diode; the output function control circuit comprises a second single chip, wherein one end of a third resistor is connected with a fifth pin of the second single chip; an eighth pin of the second single chip is connected with the circuit ground, characterized in that said LED lamp string is a two-way LED lamp string; and whererin the electronic transformer-controlled LED lamp system further comprises a fourth pin of said first single chip is connected with one end of each of a fourth resistor and a fifth resistor; another end of said first capacitor is connected with another end of said fifth resistor and connected with said circuit ground; another end of said fourth resistor is connected with said anode of said first diode; another end of said second resistor is connected with a positive pole of a third capacitor; one end of a sixth resistor is connected with a positive pole of a third capacitor and one end of a fourth capacitor; another end of said sixth resistor is connected with another end of said fourth capacitor and a cathode of said second diode; another end of said primary coil of said transformer is connected with said fourth capacitor; one end of a first secondary coil of said transformer is connected with an anode of a third diode, and a cathode of said third diode is connected with a positive pole of a fifth capacitor; another end of said first secondary coil of said transformer is connected with a negative pole of said fifth capacitor; a second end of said second secondary coil of said transformer is connected with one end of a sixth capacitor and said circuit ground, and another end of said sixth capacitor is connected with said negative pole of said fifth capacitor and said circuit ground; wherein a second pin of the second single chip is connected with one end of a seventh resistor, a third pin of the second single chip is connected with one end of an eighth resistor, a fourth pin of the second single chip is connected with one end of a key switch and one end of a ninth resistor, the other end of the seventh resistor is connected with the base of a fourth triode, the emitter of the fourth triode is connected with the circuit ground, the collector of the fourth triode is connected with the collector of a second triode, the other end of the eighth resistor is connected with the base of a third triode, the emitter of the third triode is connected with the circuit ground, the collector of the third triode is connected with the collector of the first triode, the emitter of the first triode is connected with one end of a tenth resistor; wherein an other end of the tenth resistor is connected with the cathode of a voltage-stabilizing diode and a positive pole of a seventh capacitor, the anode of the voltage-stabilizing diode is connected with the circuit ground, and the negative pole of the seventh capacitor is connected with the circuit ground; wherein the emitter of the first triode is connected with the emitter of the second triode, the base of the first triode is connected with one end of an eleventh resistor, the other end of the eleventh resistor (R 11) is connected with the collector of the fourth triode and connected with a first interface (Port), the base of the second triode is connected with one end of a twelfth resistor, and another end of the twelfth resistor is connected with the collector of the third triode and connected with a second interface (Port); wherein the LED lamp string is formed by connecting a group of LED branch circuits in parallel, and each group of the LED branch circuits is provided with one LED; or wherein the LED lamp string is formed by connecting a group of LED branch circuits in series, and each group of the LED branch circuits is composed of a group of parallel LEDs.