A circuit device for an LED's driving and stabilizing system includes an AC/DC controllable driving voltage source, a feedback driving controller, an LED demodulation driving controller controllable driving voltage source, an external regulator, and an LED modular device. While various internal conditions or factors of the circuit device may be obtained through integrally or partially setting and computing, the circuit device may also be externally connected to an input signal source according to the characteristics of different attributive conditions to thereby achieve the function of automatic regulation, enabling the LED modular device connected thereto and having been used over a long period of time to have lowered brightness attenuation rate, reduced power loss, reduced heat generation, and accordingly, extended the LED's lifespan.