Because the absence of vertical stabilizer causes neutral or slightly negative yaw stiffness, the flying wing a ircr aft differs from conventional configuration aircraft in lateral directional stab i lity. Thus in the conceptual design stage of tailless aircraft, not only aerodyn amic characteristics need to be optimized, but also the relatively accurate stab ility derivatives are necessary to analyze the dynamic stability of aircraft. It requires higher accuracy and efficiency of aerodynamic calculation program. An i mproved vortex lattice algorithm is proposed in this paper. A certain ta illess aircraft is chosen to be tested in wind tunnel and calculated with the improved algorithm. The comparison of the results shows that the improved al gorithm has made progress in accuracy during sideslip.