The effect of steam flash-explosion(SFE) on solubility and extraction of protein from thermal processed soybean meal was studied.Results obtained from the particle size and steam pressure experiments showed that when the steam pressure was low,the nitrogen solubility index(NSI) of the soybean meal was increased with increasing steam pressure;when the particle size of soybean meal was more than 100-mesh screen,the SFE had little effect on NSI and the optimum particle size for soybean meal was between 20-mesh screen and 80-mesh screen.When steam pressure was 1.8 MPa,180 s and the particle size of soybean meal was between 20-mesh screen and 80-mesh screen,the NSI of SFE-treated soybean meal was significantly improved by 1.1 times than untreated soybean meal.It was found that the protein extraction was significantly influenced by pH and temperature.Under optimal conditions the maximum protein extraction yield from SFE-treated soybean meal was 76.04%.