A method for manufacturing a chair seat, wherein borders of the chair seat is injection molded by two steps, comprises following steps: a. preparing net cloth, inner border injecting mold, outer border injecting mold, plastic and gun screw; b. injecting inner border: warming up inner border injecting mold, simultaneously heating up the plastic, and injecting the plastic into the inner border injecting mold when its temperature reaches the injecting temperature; c. installing the net cloth: cutting out the net cloth according to the size of the inner border, impacting the edge of the net cloth into the inner border by the gun screw by hand, and then cutting redundant net cloth; d. injecting outer border: inserting the inner border with impacted net cloth into the outer border injecting mold, and injecting the plastic into the outer border injecting mold when its temperature reaches the injecting temperature.