approach are useful to save the calculation cost. Both methods express the PES of some target highlevel quality (VHL) as a sum of a PES fit (VLL) to a large number of low-level points and an energy difference surface (ΔVHL-LL) between high-level and low-level methods based on much fewer data points. We proposed to employ the PIP-NN method to fit VHL and ΔVHL-LL. More importantly, we took advantage of the limited extrapolating ability of the NN to get the sampling for the ΔVHL-LL effectively. In addition, ΔVHL-LL was used to make predictions for points that were not calculated directly at the high-level method. Finally, all data points were used to fit the final PES by PIP-NN.