In this work, in order to establish a relationship between the surface properties, i.e., active surface phase composition and electronic structure, and the OER activity of the LNO with oxygen vacancy, we have employed epitaxial LaNiO3 (001) single crystalline films as models to exclude the effect of nanostructure. We prepared a series of welldefined LaNiO3 single crystal films on Nb-doped SrTiO3 (001) substrate by using a pulsed laser deposition (PLD) method. At the same time, we used two different ways to introduce oxygen defects in LNO and investigated the effect of oxygen vacancies on OER activity and stability. In addition, the surface composition and electronic structure before and after OER treatment were characterized by XPS. The results revealed that the OER performance of LNO and LNO with oxygen vacancies highly depends on the surface Ni/La ratio.