The onboard datalink system plays a significant role in civil aircraft systems nowadays. It should be developed to be faster and be equipped with higher stabilities so as to satisfy the increasing demands of communication. The onboard datalink system based on the IMA architecture is a new system and its performance has not been verified adequately. In order to verify the Required Communication Performance of this kind of datalink system, the paper designs and builds a simulation system, which including the onboard system, VHF link and the ground system. The ground system loads and records the time of 60 uplink messages and the according response messages based on the methods given in the ICAO Doc 9896. After calculating and analyzing the results, it comes to the conclusion that the datalink communication system based on the IMA architecture meets the RCP requirements.