The invention discloses a power transmission section economical power transmission power online determining method based on risk analysis and belongs to the technical field of electric power systems and automation thereof. The power transmission section economical power transmission power online determining method based on risk analysis comprises the steps that data of a power grid model are obtained online, a power transmission power section is divided equally between the upper limitation and the lower limitation of power transmission power of a power transmission section, parallel computing is conducted on the economic benefits and system safety and stability risks of power transmission under power transmission power of all values, and power transmission risk benefits under the power transmission power are computed; then, the optimal economical power transmission power value of the power transmission section is determined by analyzing and comparing the power transmission risk benefits of the power transmission power of different values. According to the power transmission section economical power transmission power online determining method based on risk analysis, the power transmission benefits and the system safety risks are taken into comprehensive consideration, the power transmission section optimal economical transmission power online determining method is provided, the effective balancing of the economy and system stability of power transmission can be achieved, the margin of the power transmission section can be fully used under the premise that system security constraints are considered, and the economy and the safety of the operation of a power system can are improved.