We measured the electronic structure of an iron arsenic parent compound LaFeAsO using angle-resolved photoemission spectroscopy (ARPES). By comparing with a full-potential linear augmented plane wave calculation we show that the extra large Γhole pocket measured via ARPES comes from electronic structure at the sample surface. Based on this we discuss the strong-polarization dependence of the band structure and a temperature-dependent holelike band around the M point. The two phenomena give additional evidences for the existence of the surface-driven electronic structure.