A pixel processing circuit, a reading method thereof and an image sensor are provided. The pixel processing circuit includes a pixel array comprising a plurality of pixel units arranged in a Bayer array, an Analog-to-Digital Converter (ADC) module comprising a plurality of analog-to-digital converters and a plurality of switch selection modules. The analog-to-digital converters are respectively located on the opposite first side and second side of the pixel array. The switch selection modules are set between the pixel array and the analog-to-digital converters to switch the connectivity between the pixel units and the analog-to-digital converters on the opposite sides of the pixel array so that signals of green pixel units are read by first analog-to-digital converters located at the first side of the pixel array, and signals of remaining color pixel units are read by second analog-to-digital converters that are located at the second side of the pixel array.