Abstract: The reserve sharing among the interconnected power systems facilitates the improvements on their anti-disturbance capability and operating economy. However, an unreasonable reserve allocation scheme may lead to the ineffective utilization of the reserve, thus increasing the potential risks. Taking the multi-area interconnected power grid as the research object, a multi-area reserve sharing mechanism is designed, and a generation-reserve joint optimization model considering security risks is built. For the risk assessment, a scenario generating, screening, and compressing method based on the Monte Carlo Simulation is proposed. This method considers the new energy, the load fluctuations and the random failures of the power generation, transmission and transformation equipment. Then, based on these compressed scenarios, the risk assessment model considering the wind curtailment penalty and the load restriction is constructed. The risk assessment results and the closed-loop iteration strategy of the joint optimization are given by establishing the reserve constraints of unit groups. Finally, the IEEE 118-bus system is taken as an example for simulation. The economic benefits and the potential risks under both the independent reserve allocation and the joint reserve sharing modes are analyzed in detail, verifying the effectiveness of the proposed method and the necessity to consider the security risks in the process of optimal generation-reserve allocation.