Improving the efficiency of frequent itemset mining in big data is a hot research topic at present. With the continuous growth of data volume, the computing costs of traditional frequent itemset generation algorithms remain high. Therefore, this study proposes a fast mining algorithm of frequent itemset based on Spark (Fmafibs in short). Taking advantage of bit-wise operation, a novel pattern growth strategy is designed. Firstly, the algorithm converts itemset into BitString and exploits bit-wise operation to generate candidate itemset. Secondly, to improve the processing efficiency of long BitString, a vertical grouping strategy is designed and the candidate itemset are obtained by joining the frequent itemset between different groups of same transaction, and then aggregating and filtering them to get the final frequent itemset. Fmafibs is implemented in Spark environment. The experimental results on benchmark datasets show that the proposed method is correct and it can significantly improve the mining efficiency.