Composite HZSM-5 with nanosheets was dynamically synthesized using the soft template method. The textural and acid properties obtained by means of XRD, SEM, TEM, N-2 sorption, NH3-TPD, and so on were characterized and their effect in catalytic cracking of mixed C-4-C-6 hydrocarbons to light olefins was investigated. Mesopores showed a positive effect on light olefin selectivity much greater than acidity. Composite samples with more mesopores and appropriate acidity exhibited higher light olefin selectivity and longer lifetime in a fixed bed reactor.