为降低物流无人机（unmanned aerial vehicle, UAV）在空中失效或者发生碰撞后的对地风险，通过构建关于物流无人机对地风险评估的模型，专注于无人机失效坠地和碰撞后的风险分析。首先，在无人机失效坠地风险模型中，详细讨论无人机在不同飞行阶段可能的失效情况，包括垂直坠落和平抛坠落，以及这些坠落对地面人员可能造成的伤亡和经济损失；其次，碰撞坠地风险模型则分析了无人机在空中相撞后的动态行为以及其对地面安全的影响，包括碰撞动量-能量守恒和碰撞后果评估；最后，构建一个综合的三维风险评估矩阵，将事故发生的可能性、地面死亡人数和经济损失结合，用以评估不同情景下的风险等级。通过案例分析表明，得到的地面死亡人数在10^-6量级内，并且得到不同区域内的风险等级。可见此方法为物流无人机运营商和相关政策制定者提供了重要的风险评估工具和数据支持。

In order to reduce the risk of logistics drones to the ground after failure or collision in the air, a model for logistics drones to the ground risk assessment was constructed, focusing on the risk analysis of drone failure and crash. Firstly, in the drone failure and crash risk model, the possible failure of drones in different flight stages was discussed in detail, including vertical fall and horizontal fall, as well as the casualties and economic losses that these falls may cause to ground personnel. Secondly, the collision and crash risk model was analyzed the dynamic behavior of drones after a collision in the air and its impact on ground safety, including collision momentum-energy conservation and collision consequence assessment. Finally, a comprehensive three-dimensional risk assessment matrix was constructed, combining the possibility of accidents, the number of deaths on the ground and the economic losses to evaluate the risk level in different scenarios. The case analysis shows that the number of deaths on the ground is within the order of 10^-6, and the risk level in different regions is obtained. It can be seen that this method provides important risk assessment tools and data support for logistics drone operators and relevant policy makers.