[Objective] To ensure the operation stability and economic requirements of the power grid under large disturbances and to incentivize market participants to engage in system protection，this paper proposes a market mechanism for emergency generator tripping and load shedding ancillary services. [Methods] First，the operational process of the proposed ancillary service market is designed，along with a two-part pricing scheme consisting of capacity and utilization fees for generator and load shedding. Then，considering specific faults，the power grid is partitioned to form a candidate set of market participants for ancillary services. Subsequently，an optimization clearing model is established with a cost-minimization objective function that incorporates expected fault occurrence frequency and average outage duration. The model also accounts for transient frequency，voltage，and synchronization stability constraints. A time-domain simulation and branch-and-bound algorithm are employed to solve the ancillary service strategy. Finally，an improved CSEE-FS case is used to validate the effectiveness of the proposed market mechanism for ancillary services. [Results] Simulation results demonstrate that the proposed ancillary service strategy can effectively restore the power grid to a stable operating state. The incorporation of fault characterization factors enables precise identification of the cost-minimizing control strategy under specific disturbance scenarios. [Conclusions] The proposed market mechanism ensures that grid security and stability requirements are met，while aligning compensation with the actual service capability of market participants. It also contributes to reducing the overall cost of ancillary services.