In the common ITO manufacturing process of TFT(Thin Film Transistor),the leakage current(I_off) of some samples is abnormally high, and these abnormal samples are subjected to the same photo-resist strip equipment. This anomaly causes the strip equipment to suspend production, resulting in a loss of mass production. It is urgent to identify the reason and solve this problem for productivity and quality assurance. Firstly, the stripper of abnormal and normal equipment are collected and analyzed, it is found that the Al ion content in the stripper corresponding to the abnormal equipment was high. Secondly, it is found that I_off will increase with the increase of stripping time in abnormal equipment. Then, it is proposed that Al ions in stripper are converted into Al₂O₃ particles adhered to the passivation(PVX) layer of TFT device during the stripping process, forming a parasitic gate effect which causes I_off to be high. Finally, a series of solutions are proposed based on TRIZ, and then verified. Experimental results show that the Al ion concentration in the stripper increases from 1×10^-8 to 2.189×10^-6, and the I_off increases from 3.56 pA to 7.56 pA. Once the stripper contains Al ions, I_off increases as the number of stripping increases. The increase of I_off can be suppressed by two measures: enhancement of the plasma treatment power before the PVX depositon and the increase of PVX thickness. In summary, it can be determined that the abnormally high I_off is caused by the parasitic gate effect formed by Al ion in stripper solution, which can be suppressed by strengthening plasma treatment before PVX deposition and the increase PVX thickness.