Abstract: This paper researches into reentry vehicle impact errors which result from the roll velocity changes by use of rotor dynamic theory.The roll regularity and balance attackangle are presented through analysis of general attackangle equation,and the impact dispersion of nonspinning vehicle is got.Steady roll impact error can be obtained when the reentry trajectory is divided into many sections.Rollpasszero(RPZ) impact error is analyzed and calculated on the basis of RPZ height.The roll resonance phenomena are discussed.The conditions of roll resonance and dispersion calculation formula are given also.Finally,Several important conclusions are presented.