Wheat flour was used as material to be extruded and made for koji of white soy sauce. The glucoamylase activity of koji is regarded as the index. The effect of different extrusion parameters on the glacoamylase activity of koji were studied. By single factor experiment, the effect of the moisture content of flour, screw speed, feeding spend and barrel temperature on the glucoamylase activity were investigated. Then the extrusion parameters were optimized by Response Surface Methodology (RSM). The results showed that the optimal glucoamylase activity was 1293.49 U/gunder the following extrusion conditions, including moisture content of 40%, screw speed of 100 r/min, feeding speed of 10kg/h, and barrel temperature of 80 °C. The koji of higher glucoamylase activity was utilized to ferment and the brewing experiment of white soy sauce was conducted by low-salt solid-state fermentation. After the end of fermentation, the contents of amino acid nitrogen and reducing sugar were 0.65 g/100mL and 243.25 mg/mL respectively in the white soy sauce. The white soy sauce tasted sweet and showed good flavor.