In order to evaluate the symmetry of a power flow Jacobian matrix， some symmetry indices are established according to the relation among the singular values of a real matrix with zero diagonal elements， the corresponding symmetric matrix and the antisymmetric matrix. The comparisons of indices include not only the comparisons of 2-norm and F-norm， but also those of the weighted sum of singular values. These indices are also applicable to complex matrix. The simulation on the IEEE 30 system shows the effectiveness of the proposed indices.