Abstract: The oil shale of the down area ES4 in the center Damingtun Depression which is wide distribution and large thickness. The ES4 depression is the most important source oil rocks and has a good tight oil reservoir, what is the key area of tight oil exploration and development in Liaohe Depression. The key factors affect the fracture extent of tight oil reservoir rock and mining effectiveness is the brittleness of rock. By transverse and longitudinal wave sonic logging data to calculate the object of the study area tight oil reservoir horizon dynamic style modulus and Poisson's ratio dynamic, application Rickman rock brittleness index calculation formula to calculate the tight oil reservoirs brittleness. On this basis, Damintun Depression ES4 tight oil reservoirs in the oil shale carbonate quality oil shale, silty shale, siltstone and shale lithology dolomites five kinds of brittleness analyzed establish superiority brittleness index lithologic sequences. The results show that the best index of brittleness shale dolomite, the brittleness index greater than 40 accounted for 92.43%. It is advantageous purpose layers of dense oil Hirai fracturing.