As an important branch of data mining, sequential patterns mining has been extensively studied. Based on sequential patterns mining, Structural Relation Patterns (SRPs) mining is proposed for mining relations among sequences, these relations are generally hidden behind sequential patterns. Upon the previous researches, the concepts of concurrent relation pattern and exclusive relation pattern are redefined; the definitions of ordered relation pattern and iterate relation pattern are given. The properties of SRPs are discussed, and they form a theoretical foundation for further study of structural relation patterns and relative mining algorithms. Beside, the thinking of mining associate relations among sequential patterns is proposed. SRPs mining is significant in practical applications same as sequential patterns mining.