The purpose of paper is to identify the root cause of conductive film bonded n-type mono Si module failed after TC200 test. Firstly, it established 2D model of CF photovoltaic module based on FEA software, which simulated the developing trend of stress concentration at distinct locations relative to ribbon on substrate of cell when temperature repeated from -40 degrees C to 85 degrees C with the rate of 40 degrees C/h. Then it compared the stress nephogram of typical position in module with various thickness of encapsulant. Meantime, the rheological property of EVA and PO investigated by TMA to distinguish the potential factors of material in changing temperature stage. EL images and microscope pictures of cross profile applied to straightforward validate the effectiveness of simulations. It concluded that the distribution of stress indicated the high risky breakage of silicon substrate happened during hypothermia stage, especially for thin EVA.