The main bottleneck in obtaining high-performance thermoelectric (TE) materials has been identified as how to decouple the strong interrelationship between electrical and thermal parameters. Herein, we present a precise interface modification approach based on the powder Atomic Layer Deposition (pALD) technology to enhance the performance of CuNi alloys. Single-layer ZnO and Al2O3 layers have been deposited on the surface of powders, typically in 10-100 cycles, and their effect on the TE performance of bulks has been thoroughly investigated. A standard model is proposed and experimentally confirmed to build the relationship between the ALD oxide cycle numbers and Zn and Al content, which could be easily adapted to other pALD processes. The enhancement of the Seebeck coefficient, caused by the energy filtering effect, compensates the electrical conductivity deterioration due to the low electrical conductivity of oxide layers. Furthermore, the oxide layers may significantly increase the phonon scattering. Therefore, to reduce the resistivity of coating layers, a multiple-layer structure is deposited on the surface of powders by inserting Al2O3 into ZnO is constructed on. The atom probe tomography shows that after pressing, the Al atoms diffused into ZnO and realized the doping effect. Al diffusion has the potential to increase the electrical conductivity and complexity of coating layers. In comparison to pure CuNi, zT increased by 227.6% as a result of the decrease in resistivity and stronger phonon scattering in phase boundaries. The study demonstrates that ALD-based interface modification may be a versatile method for decoupling TE parameters and precisely modifying phase boundaries, which is practical for other thermoelectric materials.