In this work, the crystal structure of the BiOF is studied under high hydrostatic pressure using ab initio calculations. Pressure-volume relationships and structural transitions are investigated using Siesta method. A first-order phase transition from the tetragonal matlockite PbFCl-type structure with space group P4/nmm to the orthorhombic structure with space group Cmcm is successfully observed for BiOF. This phase transition which occur around 19.6 GPa is also analyzed from the total energy and enthalpy calculations. In addition, electronic properties of BiOF are researched during the pressure. By analyzing the energy band structures, it is found that the band gaps P4/nmm and Cmcm phases for the BiOF are 2.74 and 2.47 eV, respectively.