Abstract: In order to avoid the mountain orchard monorail conveyor having a crash with the moving objects across the monorail or motionless obstacles on the monorail in front of the conveyor which was running on the monorail, and improving the conveyor's operation safety and stability, an ultrasonic obstacle avoidance system for the monorail conveyor had been developed.The system was composed of microprocessor, ultrasonic probe and its transmit-receive circuit, power module, wireless communication module, keys and so on.A series of test had been taken for testing the conveyor's operation performance.In the tests, regular objects and irregular small stones were simulated as obstacles on the monorail, tree branches and potted citrus with many lateral branches had been taken as non-obstacles beside the monorail.In each test, the ultrasonic probe was installed in three different positions on the front of the monorail conveyor respectively, and the conveyor's running speed was fixed at fast (4.32 km/h), medium (2.88 km/h) and slow(1.44 km/h) three types of different speeds.Test results showed, the obstacle-avoidance system could identify the obstacles on the monorail and the non-obstacles beside the monorail, which could promote operation safety and stability of the monorail conveyor when it run on the monorail unmanned.