A LFSRbased clockcontrolled keystream generator is presented. One LFSR picks up ten LFSRs from fifteen LFSRs whose  spans are all pair wiseprime, and the ten LFSRs will generate ten m sequences, export the sum of the m sequences, so the period of the sequence is extended. Its linear complexity, evenness, autocorrelation and the running features are also analyzed. The result shows the period of sequence produced by this generator reaches 2128and its properties are  also very good. The sequence can be encrypted as the keystream sequence.These msequences are selected randomly by the clockcontrolled mechanism, which increases the number of keystream sequences. In addition, an algorithm is proposed,and the generator is thought to be practical.