ZSM-5 zeolite was synthesized by a seed-induced strategy in a template-free gel synthesis system of high concentrations. The effects of seed size and seed amount on the morphology of the products were investigated, and the amplification synthesis was also conducted. The results show that the monodispersed and uniform ZSM-5 zeolite with a hexagonal plate morphology can be obtained via seed-induced synthesis. The size of seeds has an effect on the size of the induced ZSM-5 zeolite crystals. The smaller seeds can induce the formation of smaller ZSM-5 zeolite crystals. Meanwhile, little differences appear in the size distribution and pore structure of synthesized zeolites. The size of the synthesized ZSM-5 zeolite product decreases with the increase of seed amount, thus obtaining different sizes of ZSM-5 crystals from micron-scale to submicron-scale. The product preparation can be scaled up to 20 times and the product prepared in a larger scale preparation has good crystallinity and thermal stability. The yield of zeolite product can reach over 90%.