The surface relaxations, band structures, densities of states and surface energies of BiOCl001 surfaces containing 001-1Cl, 001-BiO and 001-2Cl are studied using first-principles based on density functional theory. The calculated results indicate that there exist obvious relaxations for the three types of 001 surfaces, especially for their double chlorine layers. The relaxation result of 001-1Cl surface is the minimum one in the BiOCl001 surfaces. Compared with the electronic structure of bulk BiOCl, BiOCl001 surfaces exhibit the smaller band gap and stronger localized energy levels. Besides, both conduction and valence band of 001-BiO shift towards the lower energy and there exist surface states at the bottom of conduction band. For 001-2Cl, surface states are located at the top of valence band. The occurrences of these surface states can lead to the obvious reductions of band gaps for 001-BiO and 001-2Cl. Furthermore, the surface energy of BiOCl001 is calculated and investigated. The analysis results show that surface energies of 001-1Cl, 001-BiO and 001-2Cl are 0.09206 J·m-2, 2.392 J·m-2 and 2.461 J·m-2, respectively. Thus the 001-1Cl possesses the minimum surface energy and the highest stability, while 001-BiO and 001-2Cl exhibit the higher reaction activities and are difficult to be exposed in the growth process of BiOCl crystal. Our obtained results provide the theoretical guidance for the further understanding of the facet-dependent photoreactivity of BiOCl, the fine manipulation of their photoreactivity, and the progress of actual application for BiOCl photocatalytic material.