Abstract: A navigation system state estimation accuracy evaluation index was proposed based on the geometric relationship between the landmark and the probe for asteroid exploration attachment section with high precision requirements. Under the condition of limited resources on board and with a large number of available navigation landmarks for the probe, the index was derived by analyzing the geometric relationship between the navigation landmarks and the asteroid probe. Combined with the Fisher information matrix, a scalar calculation method for the lower bound of the system state estimation variance was designed. The method avoided the complex matrix calculations in the traditional accuracy evaluation process and adopted the "simulated annealing-enumeration method" to optimize the selection of navigation landmarks, which ensured the system state estimation accuracy and improved the navigation landmark optimization selection efficiency. The method was applied to the optical navigation scene of the Eros asteroid probe detachment section. Simulation results show that the method can effectively improve the efficiency of navigation landmark optimization selection and system state estimation accuracy.