Ultra-large IGZO (InGaZnO) products were prone to Abnormal Display (AD) during reliability evaluation at high temperature and humidity (50 ℃/80%). The main reason was that the key device’s (M2) transfer characteristic curve (I_DS-V_GS) of GOA (Gate Driver on Array) had a serious positive shift in the evaluation. In this paper, the real working environment of GOA’s key device(M2) was simulated by pulse experiment, and the bad phenomenon of serious positive shift of transfer characteristic curve was reproduced. By setting different pulse experiments, the main influencing factor was revealed. When the device(M2) was turned off, the V_DS (pressure difference between Drain and Source) was too large, so that the oxygen vacancy VO+ in the IGZO layer migrated to the boundary of IGZO and GI (Gate Insulator) and to the Source at the same time under the electric field. Due to the electrons trapping effect of oxygen vacancy VO+, the transfer characteristic curve would eventually shift positively. It was found that the migrated oxygen vacancy VO+ can be restored after heating. In addition, without changing the IGZO film forming conditions, by reducing the V_DS pressure when the device(M2) was turned off, the ultra-large IGZO product did not occur AD defects during the reliability evaluation at high temperature and humidity for 2 000 h.