The invention discloses a power transmission section conservative stability limit determination method based on optimization calculation. The method comprises the steps: obtaining basic parameters ofa power transmission section J; obtaining an anticipated fault set M of the power transmission section; determining a minimum added value of the total power of all member lines of the power transmission section J through adjusting the power generation/load power of the transmitting and receiving end of the power transmission section when each member line j in the power transmission section and thepower generation/load of the transmitting and receiving end of the power transmission section meet preset constraint conditions and when a line m in an anticipated fault set M has an anticipated opencircuit fault and the transmission power of the member line i reaches an out-of-limit critical value; and sequentially selecting the lines, which are corresponding to the line i and expected to havethe open circuit fault, from the expected fault set M, and repeating the previous step to obtain the local stability conservative limit, determined by the member line i, of the power transmission section. The method can quickly determine the conservative limit of the power transmission section of the power grid, and is higher in speed and accuracy.