The utility model discloses a packaging box capable of being opened along a diagonal line of a box body. The packaging box comprises a box body, wherein the box body is divided into a left box body and a right box body which are axisymmetric by taking one diagonal line of the box body as a boundary; the left box body and the right box body are connected to a diagonal line at the bottom of the box body through a rotating shaft; the upper surface of the left box body is provided with a side plate capable of being turned over along the diagonal line, and the side plate is connected with a rotating shaft arranged at the diagonal line of the upper surface of the left box body; the left box body is depressed inwards along a diagonal surface to form a left cavity; and the right box body is depressed inwards along the diagonal surface to form a right cavity. Compared with the prior art, the packaging box is novel in structure and unique in design; the packaging box is uprightly arranged through the arranged side plate, so that a product in the packaging box can be shown at a certain angle, and the packaging grade of the product is increased.