Aimed at the problem that high access roundtrip delay and low throughput exist in traditional physicallayer network coding collision retransmission scheme in satellite slotted ALOHA system, an improved random network coding based collision retransmission scheme in satellite slottedALOHA systems is presented. This strategy brings in random network coding based on the physical layer network coding, through the source node data packet random coding, the receiving node utilizes Gaussian elimination method to obtain the original packet. A mathematical model of the proposed strategy is established, and the date packet format for the strategy is designed, and then the throughput and transmit delay are derived in theory. The results indicate that the strategy is effectual in resolving the collision, greatly reduces the transmission slots, and the strategy has a high throughput when the number of users is a few.  [WTHZ]Key words:[WT]satellite communications; slotted ALOHA; physical layer network coding;random network coding;throughput