The invention discloses an infrared image sensor and a forming method thereof. The method comprises the steps of providing a substrate with a CMOS (Complementary Metal-Oxide-Semiconductor Transistor) control circuit, forming a pixel structure and a plug for electrically connecting the pixel structure with the control circuit on the substrate, also forming a first sacrifice layer between the pixel structure and the substrate, forming a second sacrifice layer with a first opening and covering the second sacrifice layer on the pixel structure, with the first opening being above the plug, forming a supporting layer on the second sacrifice layer on the side wall and the bottom of the first opening, forming a second opening in the supporting layer, removing the first sacrifice layer and the second sacrifice layer through the second opening, forming a covering layer which is a transmission layer for infrared ray after the first sacrifice layer and the second sacrifice layer are removed, covering the covering layer on the supporting layer, packing the first opening and the second opening, forming a third opening between the covering layer and the supporting layer, and forming a sealing layer in the third opening through a physical vapor deposition technology, so as to seal the third opening. The covering technology in the technical scheme is compatible with the traditional semiconductor technology.