The invention relates to a bilateral negotiation transaction simulating method based on the network security constraint. In the simulating process of a bilateral negotiation transaction, the uncertainty of the transaction process is simulated by randomly establishing and deleting a transaction mode. In order to meet the power flow constraint, the power flow constraint can be considered through the user load curve and the grid power flow transfer distribution factor. In addition, the present invention also proves the convergence of the proposed bilateral negotiation simulating method and ensures the adaptability of the proposed method to the large-scale direct transaction simulation. Compared with the prior art, the invention has the advantages of incorporating the network security constraint in the direct transaction market clearing conditions, and helps to solve the problem in prior art that it is difficult to effectively carry out the safety verification of the direct electricity transaction in China at present.