SUMMARYPath diversity of different concurrent paths inevitably introduces out-of-order packet delivery, which leads to unnecessary retransmissions and a severely lowered data throughput. In order to analyze the fundamental behavior and influencing factors of packet reordering, several sets of simulation-based multipath experiments are conducted with different aggregating paths. In addition, the relationship between reordering and number of paths are discussed. Furthermore, an end-to-end measurement study of packet reordering in concurrent multipath transfer is presented. To simply the analysis process, a cumulative distribution function of transmission delay for each packet is used. The model is proved to be an effective one by contrastive analysis. Finally, some solutions to handle it are provided with a further discussion.