Hierarchical ZSM-5 zeolite was synthesized by a seed-assisted dry-gel conversion method, and the effects of seed amount, deionized water amount and crystallizing time on the structure and morphology of hierarchical zeolite were investigated. The results show that the crystallization rate of zeolite is increased with seed addition. Amorphous silica-aluminium gel can directly dissolve in the water film condensing on the seed surface and rapidly grew into ZSM-5 nano-zeolite near the seed. Simultaneously, nano-zeolites aggregate and some mesoporous channels are formed between the nano-crystals. The size of nano-zeolite and the resulting mesoporous pores can be adjusted by seed amount, deionized water amount and crystallizing time. The catalytic stability of the resulting hierarchical ZSM-5 zeolite is improved by nearly 5 times, compared with the conventional zeolite in the isomerization of styrene oxide to phenylacetaldehyde.