Given m databases D1,...,Dm of strings, the purpose of the frequent string mining is to find all strings that fulfill certain constraints of all string databases. In this paper, a useful data structure is proposed to construct suffix and LCP table which can reduce the total space consumption of string mining efficiently. We demonstrate the use of this data structure by optimizing the algorithm proposed by A.Kügel et al  and present the improved algorithm. It is achieved that the space consumption in our algorithm is proportional to the length of the largest string of all databases. A set of comprehensive performance experiments shows that the processing rate is enhanced because amount of items are reduced in new data structure.