Abstract: The effects of seed type, additive environment, additive amount and particle size of seed crystals on hydrothermal synthesis of SAPO-34 molecular sieves and the mechanism of seed were investigated by using triethylamine（TEA）as template. The results showed that SAPO-5 molecular sieves with the same AFI structure crystals could be induced by the seeds containing SAPO-5 heterocrystalline, but the pure SAPO-34 could be prepared by pre-treating the impure seed crystals with phosphoric acid for 20 h. The silicon-aluminum ratio of seed crystal has obvious influence on the yield and particle size of the synthetic product, whether added in the acidic or the weakly alkaline gel. The seeds prepared with high SiO2/Al2O3 molar ratio can improve the yield and reduce the average particle size of the product, and the etching effect of acidic system on the seeds can provide bigger surface, so that the seed induction effect is stronger. When the content of crystal seed was 0-0.5%，the yield of product was increased and D(50) was decreased with the increase of the content of seed crystal with high SiO2/Al2O3 ratio . Especially when the content of seed crystal was more than 1%, the effect of seed addition on yield and D (50) of product tended to be gentle. In addition, the small-grain products prepared by seed-assisted synthesis could continue to be used as seed inducers. The yield, average particle size, elemental composition, morphology and pore structure of the product are similar to those of the product prepared with the help of large grain seed, it lays a foundation for the stable and continuous synthesis of small-grain molecular sieves with controllable particle size.

Key words: SAPO-34, SAPO-5, seed crystal, molecular sieve, small particle