The invention relates to a stability checking method for a power transmission section in a planned operation mode, and the method comprises the steps: obtaining a power transmission section correlatedequipment list and a power transmission section list; constructing a correlation matrix between the power transmission section correlated equipment and the power transmission section; constructing atime sequence state matrix of the power transmission section correlated equipment, and determining a time sequence state matrix of the power transmission section according to a section correlation vector in the correlation matrix; carrying out the dividing of the time sequence intervals of the power transmission section according to the time sequence state matrix of the power transmission line, and determining a planned load flow limited value of the power transmission section in each time sequence interval. According to the invention, the method achieves the automatic recognition and safety checking of the limit value of the power transmission section in the planned operation mode, improves the calculation speed and precision of the safety check of the planned operation mode, and greatlyimproves the easiness and practical level of the safety check of the planned operation mode.