Abstract: Data relay satellite(DRS) system can provide excellent services to various user spacecrafts,but the inter-orbit link(IOL)between DRS and user is obviously influenced by user's altitude.The effects of circular orbit spacecraft altitude on the performance of IOL were analyzed.A mathematical model was established to calculate the extreme values of free-space loss and DRS′s IOL antenna field angle,followed by simulation demonstrations with STK6.1.Based on the mathematical model,two instances of low earth circular orbit(LEO)spacecraft and navigation satellite were given respectively.For LEO users,the extreme Lf difference is less than 4dB and antenna field angle is within ±13° to which there is no need to pay attention during design,while for navigation satellite user,they are 15dB and larger than 35°which result that some relevant methods should be adopted to prevent over-design and antenna with large field angle should be employed on DRS.