A mobile phone proofed against water, dust, and physical shocks (tri-proofed) has a structure comprising a first casing, a second casing, and a third casing. The first casing is provided with protrusions, and the third casing is provided with convex blocks. The second casing is provided with a first groove for a protrusion, and is provided with a second groove for a convex block. The protrusions and the convex blocks are both interference fits in the grooves. Moreover, the second casing also includes cosmetic surfaces. The first casing and the third casing have outer surfaces and each cosmetic surface protrudes out of the outer surfaces. The cosmetic surfaces are in first contact when the mobile phone is dropped. Waterproofing, dustproofing, and shockproofing are simultaneously achieved with the single second casing structure.