Abstract: In order to provide relay communication supports for future Chinese lunar exploration program，Queqiao-2 relay communication satellite was developed.Queqiao-2 can perform scientific observations with three kinds of scientific instruments on board.The system design of Queqiao-2，including mission orbit and transfer orbit design，configuration and layout design，housekeeping and information flow design，power supply and distribution design，GNC and propulsion system design，communication links design，etc.，was accomplished through comprehensive tradeoff and evaluation on technical maturity，availability，schedule，cost，and so on.With a view to reducing development risk，both the platform and relay communication payloads were developed based on significant heritage from previous Queqiao relay satellite and other relevant spacecraft.Queqiao-2 features flexible system architecture to support multiple frequencies，modulations，data rates and software reconfigurations to meet new user requirements.Subsequent to a successful launch on March 20，2024，by means of 5 orbit maneuvers，Queqiao-2 was inserted into a highly elliptical frozen mission orbit around the moon with a 24h period on schedule.Following on-orbit tests and calibrations，Queqiao-2 has possessed the capacity to provide reliable relay communication services to multiple lunar exploration missions，as well as the capacity to perform scientific observations.Under the support of Queqiao-2，Chang′e-6 achieved its ambitious mission goal to collect  and return samples from the moon′s mysterious far side.In the meanwhile，Queqiao-2 has also paved the way for the following Chinese lunar exploration missions including Chang′e-7 and Chang′e-8.The design life time of Queqiao-2 is more than 8 years.Benefit from flexibility and extensibility of relay communication system design，it is convenient to provide relay communication services for future lunar exploration missions of both China and other countries.In addition，innovative scientific observations would be performed during the period that no relay communication task is arranged.The system design of Queqiao-2 reflects the development philosophy of technical innovations and inheritance integration.Based on highly flexible and extensible system architecture，multiple and concurrent relay communication mission requirements can be met.It can provide strong supports for future lunar exploration missions.Successful launching，orbit entering and on-orbit tests of Queqiao-2 verified the correct design principle and versatility.By means of Queqiao-2，more innovative scientific outcomes are anticipated and lunar exploration activities can be facilitated.

Key words: lunar explorations, relay communication, Queqiao, system design, test, validation