SAPO-34 molecular sieves with different phosphorus content were prepared by adjusting P2O5/Al2O3 molar ratios in starting gel. The crystal patterns, crystallinity, crystal morphology, element composition, functional group and thermal stability were characterized by XRD, SEM, XRF, FT-IR and TGA. It reveals that the properties and Si substitution mechanism of the framework can be changed with P2O5/Al2O3 molar ratio. Sample with P2O5/Al2O3 molar ratio of 1.5 possess the highest crystallinity and smooth cubic crystals. In addition, SP-1.5 has the lowest external surface area, the largest micropore surface area and the average pore diameter. With P2O5/Al2O3 molar ratio of 1, Si atoms directly replace P atoms during the crystallization of SAPO-34 with the formation of Si( 4Al) species. When the P2O5/Al2O3 molar ratio is lower than 2, the Si substitution mechanism can be attributed to double substitution of SM2 and SM3. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.