Abstract: Aiming at the deficiency of the existing Apriori algorithm,an improved Apriori algorithm based on compressed matrix called NCM_Apriori_1was proposed．The improvements of this algorithm are as follows:(1) adding two arrays to record the counts of 1in the row and column,so that the number of scanning the matrix can be reduced during compressing,(2)deleting the unnecessary itemsets which can’t be connected as well as the infrequent ones in compressing matrix to minify the scale of matrix and improve space utilization,(3)changing the condition of deleting the unnecessary transactions to reduce the errors of the mine result,and changing the stopping condition to make the number of cycle decreased．Algorithm performance analysis and experiments results prove that the improved algorithm can mine frequent itemsets effectively and has better efficiency of computing than existing Apriori algorithms based on compressed matrix.

Key words: Data mining,Frequent itemsets,Apriori algorithm,Compressed matrix