The invention discloses a cardinality estimation method aiming at streaming big data. The method is characterized in that cardinality estimation efficiency is increased by lowering calculation precision; partition calculation is performed on the intermediate statistical information needed by as HyperLogLog Counting algorithm, an efficient Hash algorithm and an optimal bucketing number are selected, an improved bucketing method is used to evenly map hashed data into different bucket numbers, increment maintenance is performed, and combination is then performed to obtain the final intermediate statistical information so as to calculate a cardinality estimation value. The method has the advantages that historical data is effectively utilized, repeated calculation is avoided, and the cardinality estimation efficiency is increased greatly; high-precision cardinality estimation is achieved, and the efficient bucketing method is provided as compared with a traditional algorithm; the algorithm is quite low in space complexity, and calculation resource consumption is lowered.