With the problem that low fiber utilization in the alcohol process from maize straw，the influence of extrusion system parameters on fiber content of maize straw (cellulose, hemicellulose and lignin) through square combination experiment of five factors and five levels with orthogonal rotation by the single extruder，these parameters include the nozzle’s gap(B), distance(δ) between screw end and internal surface of die, the temperature(Τ) of sleeve, the screw speed(N) and straw moisture(W). The optimum values of parameters of extrusion system were put out. They were as follows: B=4 mm，δ=5 mm，T=120℃，N=90r/min，W=20%, and on the optimus parameters, fiber content of maize straw were follows: cellulose content is 3511%, hemicellulose content is 31.83%, lignin content is 6.77%. If the parameters of extrusion system were selected reasonably, the test results could provided certain reference for extruding pretreatment process of producing alcohol by straw fiber. 