In the present study,we have fabricate d a heterojunction Si/NiO:Na diode by magnetron sputtering method.The X-ray dif fraction (XRD) results show that only one diffraction peak appears for NiO:Na films on Si substrates,which is corresponding to (111) N iO:Na preferred orientation and indicates that NiO:Na belongs to cubic structure.When O₂/Ar+O_2ratio changes from 0% to 30%,there is no obvious change about (111) diffraction peak position,but the (111) peak in tensity has been improved greatly, which means that the introduction of oxygen is benefit for the NiO:Na film cryst allization.When further increasing O₂/Ar+O_2ratio to 60%,the (111) peak shifts to left,indicating that c axis d istance increases.This phenomenon can be explained that Ni depletion or oxygen vacancies may be complemented through i ntroducing oxygen atmosphere. The (111) peak reversely shifts to larger diffraction angle when sputtering NiO: Na film in pure oxygen atmosphere, which may result from the excessive oxygen defects.From I-V curves,the electr ical properties show that when changing O₂/Ar+O_2ratio from 0% to 30%,Si/NiO:Na heterojunction shows the be st rectifying property,where its V_oc is 4.9V and the leakage current appears until the negative voltage reaches －7V.It may be explained by that the crystallization of NiO:Na thin films has been improved and their defects decrea se.When further increasing O₂/Ar+O_2ratio,both the crystallization qualities and rectifying properties of NiO:Na thin films are weakened. Considering the results of XRD,atomic force microscope (AFM),UV and I-V characteristics,it can be concluded that the partial introduction of oxygen atmosphere is beneficial to the crystal structure and reduces the crystal defect ,causing the improvement of the electrical properties of Si/NiO:Na pn junctions.