An adaptive clock signal generator with noise immunity capability is disclosed, including a gain amplifier for processing an analog oscillation signal to generate an amplified signal; an adjustable Schmitt trigger, coupled with the gain amplifier, for generating a triggered signal according to the amplified signal; an output buffer, coupled with the adjustable Schmitt trigger, for generating a clock signal according to the triggered signal; and a noise detector coupled with the adjustable Schmitt trigger. The noise detector detects noise components of an input signal and enlarges the hysteresis window of the adjustable Schmitt trigger as the level of detected noise increases.