A protective shell for a mobile phone with a detachable external camera lens, the protective shell comprising a housing body formed with a position hole for a built-in camera of the mobile phone, the protective shell further comprising an external camera lens assembly, and the external camera lens assembly comprises a lens mount, provided thereon with a first stepped hole and several optical lenses surrounding the first stepped hole; a pivoted positioning element, provided with a first detachment prevention structure and a second detachment prevention structure respectively at both ends, with a rotary positioning portion in the middle, wherein, the rotary positioning portion is located in the first stepped hole, the first detachment prevention structure and the second detachment prevention structure are respectively located at both ends of the first stepped hole, for limiting the lens mount on the rotary positioning portion, and the second detachment prevention structure is connected with the housing body; a first elastic member, arranged between the first detachment prevention structure and a step of the first stepped hole, with a bias pressure applied on the lens mount; and a first positioning structure, comprising a first positioning portion and several first positioning and fitting portions, which are arranged on both the lens mount and the housing body, or on both the lens mount and the second detachment prevention structure; wherein, when under the action of an external force the lens mount is adapted to move away from the housing body in the axial direction of the pivoted positioning element, so that the first positioning portion is detached from the corresponding first positioning and fitting portion against the elastic force of the first elastic member, and the lens mount is adapted to rotate relative to the housing body under the external force, and when the lens mount rotates to a point where the selected optical lens is aligned with a position hole for the built-in camera and the external force disappears, the lens mount is adapted to enable the first positioning portion to be aligned and attached with the corresponding first positioning and fitting portion under the elastic force of the first elastic member, thereby limiting the rotation of lens mount relative to the housing body; the external camera lens assembly is connected with the housing body in a detachable manner and characterized in that the housing body is provided with a chute with its both sides provided with a guide rail; the second detachment prevention structure of the pivoted positioning element is adapted to enter or exit from the chute through one end thereof, and move along the guide rail back and forth, and the pivoted positioning element is provided with a mounting groove in the axial direction; and a second positioning structure, provided on both the second detachment prevention structure and the chute, comprises an elastic positioning component limited in the mounting groove, and at least one second fitting and positioning portion arranged at the bottom of the chute, the elastic positioning component comprises a second positioning portion and a second elastic member, under the elastic force of the second elastic member the second positioning portion partially extends out of the mounting groove and fits with the corresponding second fitting and positioning portion, thereby preventing movement of the second detachment prevention structure in the chute.