The invention is applicable to the technical field of dimming, and provides a dimming circuit needing no distinguishing of input and output and a
lighting system. The dimming circuit comprises a filtering module, a rectifying module, a
signal control module and an MOS driving module. The rectifying module supplies power to the
signal control module and the MOS driving module. When a first end of the filtering module is connected with a live wire and a third end of the filtering module is connected with a lamp, the
signal control module sends a first dimming signal to the MOS driving module according to
user input, and the MOS driving module outputs a dimming
voltage to the third end of the filtering module according to the first dimming signal. When the first end of the filtering module isconnected with the lamp and the third end of the filtering module is connected with the live wire, the signal control module sends a second dimming signal to the MOS driving module, and the MOS driving module outputs a dimming
voltage to the first end of the filtering module according to the second dimming signal. According to the invention, single-zero- / live-wire compatibility is realized, the live wire and the load wire do not need to be distinguished, the dimming circuit can work under random wiring, the operation is convenient, and the problem that normal work cannot be realized due to wrong wiring is avoided.