Provided are a TRIAC dimmer detection circuit, chip and method, and an LED driving chip and system. A bus voltage reflecting signal is received, and a TRIAC dimmer detection signal is generated according to the bus voltage reflecting signal, a first reference voltage and a second reference voltage, the dimmer detection signal being used to detect whether a dimmer exists and to determine the type of the dimmer. The TRIAC dimmer detection circuit, chip and method, and the LED driving chip and system consistent with the present invention can detect whether a TRIAC dimmer is contained in an LED illuminating system, so as to determine a working state of a bleeder, thereby reducing the power consumption of the entire LED illuminating system and improving the efficiency thereof.