To address the issue of Unmanned Aerial Vehicles (UAVs) flight safety in urban spaces，the “flight in separated air corridors” mode is put forward.The safety limit for each type of UAV is defined as the vertical width required for the conflicting UAVs to avoid each other within these corridors，and it serves as the basis of corridor demarcation.The core of the algorithm is Velocity Obstacles (VO).To eliminate the overly conservative assumption of the classic VO circular domain，which causes overly large safety margins，this paper proposes a dynamic elliptical protection domain based on the relative positions of the conflicting UAVs and its adaptive algorithm. To prevent overly large safety margins for long corridors and avoid deviations from the original route after obstacle avoidance，this paper designs a fast and smooth trajectory restoration control method that also eliminates velocity oscillations.The simulation experiments under two preset scenarios demonstrate that the elliptical domain not only maintains the same safety interval as the circular domain，but also requires smaller safety margins on the corridors' boundary.This contributes to real-time obstacle avoidance capability and a reduced diversion distance.