The invention discloses a sodium bentonite waterproof blanket and a construction method thereof. According to the sodium bentonite waterproof blank, a polygonal columnar flow guide groove is formed between fabric face cloth and fabric bottom cloth; a frame of the flow guide groove defines a cavity; a plurality of through water permeable holes are formed in the upper edge of the frame; a distance is reserved between the lower edge of the frame and the fabric bottom cloth; the frame is filled with quick set dry-mixed mortar; and the space between the fabric face cloth and the fabric bottom clothand the space defined by the flow guide groove are filled with sodium bentonite powder. When the sodium bentonite waterproof blanket is used, accumulated water on the surface of a water permeable concrete pavement or slope or the like can seep into the fabric face cloth of the sodium bentonite waterproof blanket, the through water preamble holes are formed between the fabric face cloth and the cavity of the flow guide groove, thus the seeped water can enter the cavity to drain away, and the problem that the accumulated water remaining between the sodium bentonite waterproof blanket and the concrete pavement or the slope causes soaking damage to the concrete pavement or slope is solved.