| The Consultative committee for space data systems (CCSDS) File delivery protocol (CFDP) is a pro- tocol speci¯cally designed to meet the comprehensive re- quirements of space networks. However, CFDP's retrans- mission mechanics in deferred mode reduce its link utiliza- tion in space networks where long propagation delay and high bit error rate exists. In this paper, we proposed an improved ¯le delivery protocol called Relayed ¯le delivery protocol (RFDP). RFDP adopts a relay transmission me- chanics which raises the link utilization and reduces the total ¯le delivery time. In the next place, we analyzed and deduced the performance expressions of both protocols. Finally, we made simulations to both CFDP and RFDP. The results show that RFDP have performance superior- ity over CFDP in space networks.