The invention discloses a pretreatment method for effectively saccharifying lignocellulose, particularly discloses a pretreatment method of lignocellulose with room-temperature light-concentration lye, characterized in the method comprises the steps of coarse grinding, lye wetmilling, alkali recovery and enzymolysizing. The ground lignocellulose is mixed with univalent metal lye having a concentration of 0.1% to 3%, solid and liquid are separated under room temperature after wet grinding, wherein the liquid is used for recovering univalent metal lye, and the solid, namely the modified lignocellulose, is used for further enzymolysizing for preparing liquid glucose. According to the invention, lignocellulose is used as the raw material, room temperature condition without external heating can be selected, low-concentration lye is pretreated, the lye can be effectively recovered, the enzymolysis efficiency is improved, the glucose yield is increased, the cost is lowered, the economical efficiency is enhanced, and drawbacks of high energy consumption, low glucose recovery rate, and high equipment requirements in current lignocellulose pretreatment method are made up.