Traditional transmission line imbalance tension calculation algorithm is studied and factors which affect traditional algorithm’s convergence are analyzed.A new imbalance tension calculation algorithm with mending steps is studied.And the methods of initial value selected and step mended are studied and the flow chart of the program is presented.Every span’s tension in one section segment under 11 kinds of operating conditions are calculated.The same result is obtained using 2 algorithm.But the efficiency of mending steps algorithm is improved greatly.