Taking the annual and monthly contract transactions of Northeast Electricity Market as background， the security correction problems for these two transactions are studied. Considering the shortage of the current methods and the medium and long-term transaction characteristics， linear programming is proposed to handle the security correction problems. the Optimization model is set up with the security constrains for different optimized bidding objectives by taking the flowgate transmitted energy as the optimized variable. The bidding results are obtained and the security correction and the congestion management are implemented at the same time. For the situation that the linear optimization problem has no solutions， a two sub-optimization conception is proposed， that is， during the first sub-optimization process， the optimization model is set up to get the feasible solution domain， then in the second sub-optimization process， the optimal solution is obtained from the feasible solution domain that is got by the first sub-optimization. Thus the proposed method is guaranteed to be feasible for actual engineering application.