The specific contact resistance, thermal stability and optical reflectivity of the ohmic contact on p-GaN of Pd/NiO/Al/Ni reflective electrode were investigated. Compared with the traditional Pd/Al/Ni electrode, the ohmic contact of Pd/NiO/Al/Ni electrode keeps low specific contact resistance (＜5×10-4Ω·cm2) and high reflectivity (＞80%@365nm) after annealing at 300℃ for 10 minutes in nitrogen environment. The optimized Pd/NiO layer thickness is 1nm/2nm. Under such conditions, the Pd/NiO/Al/Ni reflective electrode can not only form good ohmic contact, but also have low specific contact resistance, reduce the absorption of UV light and maintain high reflectivity. The results show that the appropriate thickness of NiO layer can effectively prevent the infiltration of the upper layer of Al metal into the surface layer of p-GaN during annealing, which is very important for the preparation of high-quality Al-based reflective electrode.