To improve the gel properties of commercial soy protein isolate(SPI),we introduced heat process in the traditional alkali soluble acid sinking preparation of SPI using defatted soybean flour as the raw material.The effects of heat treatment on the gel properties of soy protein isolate were studied.The results showed that heat treatment can improve gel properties of SPI.In the alkali soluble and acid sinking stage,with the increase of temperature,the gel hardness presents first increases and then decreases.In the neutralization stage,the gel hardness increases with the increase of heating temperature and processing time.The best technological condition is heating treatment in the alkali soluble stage under 60℃ for 1 h while under 40℃ in the acid sinking stage for 15 mins and under ambient temperature in the neutralization stage,the gel hardness can improve 131 percent.