A hex wrench improved structure comprises a body, one end thereof has six equally divided planes, an abutting angle is formed between each of the two planes, at least one of the planes is disposed with a groove, the groove has two inclined surfaces, one side of each of the two inclined surfaces is connected to the abutting angle of the two planes, another sides of the two inclined surfaces are connected to each other, and an obtuse angle is included between the two inclined surfaces; thereby, the hex wrench can be pressed tightly against an inner wall surface of a hole in a screw for inserting a cap screw tool to apply force, so that the hex wrench is not easy to slip, and it is easier to turn and lock or adjust the screw.