1. An external hard disk box, used for installing a hard disk, wherein there is a first fastening hole and a second fastening hole on a bottom and two sides of the hard disk, the external hard disk box comprising: a lower cover having a receiving space for receiving the hard disk, wherein there is a first positioning portion that corresponds to the first fastening hole on the bottom surface of the receiving space; an upper cover covering the lower cover; and at least one positioning structure located on one side of the receiving space, wherein the positioning structure has a second positioning portion that corresponds to the second fastening hole.
2. The external hard disk box as claimed in claim 1, wherein the positioning structure is located on one side of the hard disk, the first positioning portion is plugged into the first fastening hole, and the second positioning portion is plugged into the second fastening hole.
3. The external hard disk box as claimed in claim 1, wherein the positioning structure is a flexible flake, the flexible flake has a side board, and the second positioning portion is located on the side board.
4. The external hard disk box as claimed in claim 1, wherein the positioning structure includes an external mask, a spring flake, and a pushing element, the external mask has a through hole that corresponds to the second positioning portion, one end of the spring flake is connected with the external mask, a second end of the spring flake is a free end and has the second positioning portion, and the pushing element is slidably located in the external mask and contacts the second end of the spring flake.
5. The external hard disk box as claimed in claim 1, wherein the positioning structure is a flexible element, one side of the flexible element bends to form a linking flake, one end of the linking flake is a free end and forms a pushing portion, and the pushing portion extends to form the second positioning portion.
6. The external hard disk box as claimed in claim 5, wherein the upper cover is slidably assembled with the lower cover, two leg columns extend from two sides of the bottom surface of the upper cover, and the leg column corresponds to the pushing portion.
7. The external hard disk box as claimed in claim 6, wherein there is a first wedged portion and a second wedged portion on the lower cover and the upper cover.
8. The external hard disk box as claimed in claim 5, wherein each of the flexible elements bends upwards to form at least one curved portion, and the curved portion pushes and contacts a bottom surface of the upper cover.
