This new PIP-NN based Δ-ML approach is then applied to develop the globally accurate fulldimensional PES of the self-reaction of HO2 (HO2 + HO2) at its leading triplet electronic state. First, we constructed a low-level PES fit to 75300 points at the UM06-2X/AVTZ level. UM06-2X/AVTZ 213 was chosen as the most properties of the stationary points have the smallest deviations, compared to those calculated by UCCSD(T)-F12a/AVTZ. This is beneficial for developing the correction PES as cheap as possible. The next step is to build a correction PES. 1500 points were first chosen from the DFT dataset and then their electronic energies were re-calculated at the UCCSD(T)-F12a/AVTZ level.