Abstract: A navigation system state estimation accuracy evaluation index is proposed based on the geometric relationship between the landmark and the probe for asteroid exploration attachment section with high precision requirement. Under the condition of limited resources on board and with a large number of available navigation landmarks for the probe, the index is 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 is designed. The method avoids the complex matrix calculations in the traditional accuracy evaluation process and adopts the "simulated annealing-enumeration method" to optimize the selection of navigation landmarks, which guarantees the system state estimation accuracy and improves the navigation landmark optimization selection efficiency. The method is applied to the optical navigation scene of the Eros asteroid probe detachment section, and simulation results show that the method can effectively improve the efficiency of navigation landmark optimization selection and system state estimation accuracy.