Based on analysis of an air borne data-relay system (ADRS) and its antenna control characteristics,an ADRS is designed,using a real data receiver to demodulate and output data,and software to simulate the characteristics of antenna motion and wave beam. Two embedded computers are cooperated to finish the simulation task,with a fast Ethernet network and RS-485 field bus. The ADRS simulator features the ability of operation at every single node and fast response. It is a hardware-in-loop simulator and pass test of reliability,maintainability,testability,supportability and works well in real usages.