A tourniquet is presented with a strap including two patterns of cavities and ridges on top and bottom surfaces respectively. The pattern includes a plurality of spaced cavities arranged in parallel rows, the cavity being rectangular and including two first slopes on two short sides respectively and two second slopes on two elongated sides respectively, the first slopes having an elevation greater than that of the second slopes, and the second slopes having an inclined degree greater than that of the first slopes; and a plurality of spaced depressions arranged in parallel rows, the depression being adjacent to the cavity widthwise, the depression being rectangular, and the depression including two third slopes on two short sides respectively and two fourth slopes on two elongated sides respectively. Depths of the cavity and the depression are different.