In order to solve the problem of high temperature vertical crosstalk in large size thin film transistor liquid crystal display (TFT-LCD) quickly, the quantitative relationship between leakage current and V-CT phenomenon was studied to provide guidance of the process adjustment of TFT characteristics. Firstly, based on the contour map of Vgl_TCON characterized the occurrence of V-CT and the leakage current of TFT in actual working state, a method was developed to characterize the relationship between leakage current and severity of V-CT quantitatively. Secondly, according to the study of V-CT in CT-SEC image, the following conclusions are obtained: (1) the contour map and the trend of Ioff_total match well in different Vgl_TCON value; (2) V-CT is strongly correlated with the leakage current under the photo Ioff(Vgl_GOUT-Vpixel_255-) over any period in high temperature.