The present invention discloses a method for inhibiting the electric crosstalk of back illuminated CMOS image sensor. This invention comprises, two ion implanting layers are implanted at the different area of the backside of the pixel unit after the thickness of the backside of CMOS image sensor is reduced. The ion concentrations implanted into the two layers are controlled to decrease progressively from top to bottom. An electric field is formed from top to bottom inside the epitaxial layer. The said electric field absorbs the incident light which arrives at the substrate region outside of the space charge of the photodiode. It reduces the electron diffuses in different pixels. Consequently, it reduces the electric crosstalk of pixels, improves the manufacture process and improve the image quality of the of CMOS image sensor.