Abstract: In-situ velocity measurements which were carried out at a set of wells about 400 meters deep in the Jilin provincial oil field in 1982 indicate that anisotropy of P-wave velocity is distinct. Based on in-situ geological study in the field, analysis of rock samples and the anisotropy of permeability of cores, it is pointed out that the anisotro-py of P-wave velocity is mainly caused by faults and directional of cracks; and the orientation of cracks is correspondent with the stress state in the Song Liao basin.