An analog-to-digital signal processing method applied for an image sensor includes: providing a global analog-to-digital converter (ADC) capable of converting analog signals of all pixels of a pixel array into digital signals; providing a column-parallel ADC capable of respectively converting a plurality of analog signals of a plurality of pixels on different columns of the pixel array into a plurality of digital signals by using a plurality of ADC circuits; and, dynamically selecting and switching to enable one of the global ADC and column-parallel ADC to perform analog-to-digital conversion for analog data/signals of pixels on the pixel array.