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This study investigated the relationship between nitrogen soluble index (NSI), bulk density, gel storage modulus of soybean protein isolate and torque during high‐moisture (50%) extrusion, and analyzed the influence to extrudate texture by the moisture content and the expansion degree of extrudate. The results showed that in the range of NSI of 21–74%, bulk density of 0.41–0.47 g/cm3, and gel storage modulus of 3,800–5,400 Pa, the torque and specific mechanical energy raised with the decrease in NSI and the increase in bulk density and gel storage modulus. The lower the moisture content of the extrudate was, the higher its hardness. Interestingly, as the extrudate expands, bubble cavities formed on the surface of the extrudate could cause its hardness to drop from 13,124 g/s to 11,736 g/s and 4,840 g/s. Overall, the hard extrudates can be produced from soy protein isolates with low NSI (<21%), high bulk density (>0.47 g/cm3), and gel storage modulus (>5,380 Pa) via high‐moisture extrusion, at the same time appearing in an expanded structure that reduces the hardness test value of the extrudate. [ABSTRACT FROM AUTHOR]