The invention provides a hash mapping storage method for second flow thickness control. According to the method, second flow thickness control calculation is realized, a data structure of a hash tableis used, inlet thickness measurement values needed in the second flow calculation process are stored in the hash table with the fixed length, the advancing length of a strip serves as a keyword, a hash function is used for calculating a storage index, the thickness value of an inlet entering a roll gap at present is retrieved, and the method participates in calculation of a second flow controller. According to the method, a traditional first-in first-out queue data structure is replaced by a hash table data structure, when the currently used entrance thickness value is retrieved, only one-time calculation is needed, the shifting operation needed in the first-in first-out queue is omitted, the retrieval efficiency is high, the calculation time is short, and the method can be used for entrance thickness calculation in second flow thickness control.