Abstract: Kinetic impact is a means to deflect near-Earth asteroids（NEAs）and to reduce the risk of Earth being impacted by asteroids.An orbit optimization method for spacecraft departing from a large elliptical Earth parking orbit is proposed.Based on genetic algorithm，an optimization model is constructed，which takes the maximum deflection distance of the asteroid as the objective and considers nonlinear constraints on transfer time and fuel of spacecraft.Taking the asteroid 2019 PDC as the object，the genetic algorithm is used to optimize the global optimal solution of the departure date and transfer time of the spacecraft，and to calculate parameters of the large elliptical Earth parking orbit，Earth escape orbit and interplanetary transfer orbit.Meanwhile，Pork-chop plot of the asteroid deflection distance to departure date and transfer time is obtained using the traversing method，which verifies the effectiveness of the optimization algorithm.Results show that the proposed kinetic impact scenario and orbit optimization method can effectively deal with asteroids with diameters of 100 meters and a warning time of several years.The orbit design method and defense scenario proposed can provide a reference for NEAs defense，and lay a foundation for further precise design of spacecraft orbit parameters and implementation of engineering in-orbit verification.

Key words: near-Earth asteroid, kinetic impact, orbit optimization, Earth parking orbit, genetic algorithm, asteroid deflection