A dust-proof safety hook contains: a body, a connection shaft, a returning element, a housing sleeve, a resilient element, a rotary sheath, and a positioning bolt. The body includes an accommodation space, an opening, a first segment, and a second segment. The connection shaft includes a first part and a second part, and the returning element is mounted between the body and the connection shaft. The housing sleeve includes a slot which has a limiting portion and two notches. The resilient element is fitted with the connection shaft, and the rotary sheath includes a through orifice and a cut. The positioning bolt is inserted into the through orifice of the rotary sheath and the limiting portion of the slot of the housing sleeve, such that the rotary sheath moves along the slot of the housing sleeve by way of the positioning bolt.