In view of the inadequacy of the present swing blocking method in practice，a scheme for swing blocking based on power angle calculation is studied.The system operation power angle at the moment of the second fault is taken as a basis of identifying the degree of oscillation and combined with the boundary criterion determined by the instability condition.Then the distance protection is allowed to be rapidly applied when the calculated angle is lower than the threshold during swing blocking.Research results show that the novel criterion is simple，clear and able to quantitatively reflect the process of the oscillation as well，thus improving the performance of distance protection in swing blocking.The discussion on the amplitudes of voltage at the two ends being not equal has enhanced the reliability and applicability of the scheme proposed.Finally，simulation results based on PSCAD/EMTDC show the correctness of the novel scheme.