Abstract: The present invention disclosures an image sensor structure and a formation method thereof, wherein comprising: a pixel unit array, a peripheral circuit set at the periphery of the pixel unit array, and a composite shield structure around the pixel unit array and between the pixel unit array and the peripheral circuit, the composite shield structure comprises a light shield structure and a heat shield structure; wherein, the light shield structure comprises a metal isolation structure around the pixel unit array for isolating light emitted by the peripheral circuit, and the heat shield structure comprises a cavity set inside the metal isolation structure, the cavity is filled with a thermal isolation medium for preventing heat transfer to the pixel unit array. The present invention can avoid image quality deterioration and distortion caused by light and heat of the peripheral circuit of the image sensor.