The smaller the size of the Bi₂Te₃-based micro thermoelectric device, the more significant the effect of interface bonding strength and contact resistance on the mechanical properties, open circuit voltage and output power of the device. It is of great significance to develop a thermoelectric unit preparation technology with low cost and simple process, and to enable the interface between n-type Bi₂Te₃ bulk materials and barrier layer with low contact resistance and high bonding strength. Here, surface of n-type Bi₂Te₃-based thermoelectric material was treated in mixed acid solution (pH~3), followed by electroless plating Ni (5 μm), and then welded with Cu electrode to prepare thermoelectric unit. After corrosion, the anchoring effect between large gully on the surface of n-type Bi₂Te₃-based thermoelectric materials and Ni barrier layer contributes to the interface bonding strength of 15.88 MPa for the material corroded for 6 min. Furthermore, nano-holes between the Ni barrier layer and the fine branches corroded by further corrosion significantly increase the interface contact resistance, resulting in 2.23 μΩ?cm² for the material corroded for 2 min. Finally, the output power of the micro thermoelectric device prepared by n-type Bi₂Te₃-based bulk material for 4 min corrosion treatment is as high as 3.43 mW at 20 K temperature difference (306 K at high temperature end and 286 K at low temperature end). Compared to device with the same size prepared by commercial electroplating coating, the output power is increased by 31.92%. This work provides support to optimize the performance of micro thermoelectric devices.