ADS-B has a wide working range, and when it is applied to the collision-avoidance system in aviation, it builds a protective zone outside the previous collision-avoidance zone to avoid any collision from happening in advance, which further improves the performance of the collision-avoidance system.The detection of route conflicts is the premise of avoiding collision in advance, and the relevant algorithms are complex.To solve the problem, an algorithm of route conflict detection was proposed based on time-axis mapping.First, this algorithm interpreted route conflict as an issue of calculating the conflict intervals on the X, Y and Z axis respectively.Then, the conflict intervals on the X, Y and Z axis were mapped onto the time axis to get the conflict time periods.Finally, the intersection of the three conflict time periods was calculated to determine the route conflict.In the simulation, a detection test for the route conflicts of the invading aircrafts was conducted in the ATC collision-avoidance area within 100 nautical miles of the ADS-B working range.The results showed that only 1‰ of the invading aircrafts were in conflict, which was close to the volume ratio between the ATC collision-avoidance area and the 100 nautical miles of the ADS-B working range.Therefore, the correctness of the algorithm is proved.