Fractured horizontal wells are increasingly widely used in tight oil reservoirs with low permeability. However，most studies on drainage radius are primarily associated with vertical wells while few studies on horizontal wells. With the case of Changqing oilfield，the fractures in the horizontal wells generated by stimulated reservoir volume fracturing were simulated by band source. Pressure distribution equations of stimulated reservoir volume fracturing for horizontal wells are derived considering threshold pressure gradient，and drainage radius of fractured horizontal wells in tight oil reservoir can be studied. The results show that drainage radius first increases and then decreases with development time increasing，and drainage radius increases slightly as length of horizontal well increases. The hydraulic fracture half-length exerts different influence on drainage radius in the horizontal and vertical direction respectively，which shows that the horizontal drainage radius increases and the drainage radius of matrix and vertical drainage radius decrease as the increase of hydraulic fracture half-length. Increase of network width helps expand the drainage radius in the both directions，but its effect on drainage radius gradually becomes weaker.