A risk assessment method based on Monte-Carlo is proposed to solve the safety problem of UAV system when entering the integrated airspace to perform different tasks.Firstlythe factors affecting the ground impact events of the UAV system in the fused airspace are analyzed.Thenthe parameter distribution is used to describe the uncertainty of each influencing factor.Finallytwo typical UAVsnamelyFirebird and Typhoon Hare selected to conduct safety assessment using Monte-Carlo simulation algorithm in the low-risk areathe general risk area and the high-risk areaand the sensitivity analysis of each influencing factor is carried out.Simulation shows that different types of UAV system under different operation environment have big differences in safety target leveland UAV falling down angle is the key factor influencing the allowed failure rate.The method provides a feasible way of thinking for operational risk evaluation when UAV system entering the integrated airspaceand can enhance UAV safety level.