An installing device for an unlocking assembly comprises an upper sliding rail positioning jig, a snap spring positioning assembly located above the upper sliding rail positioning jig, and an unlocking assembly push-in mechanism located on the lateral side of the upper sliding rail positioning jig. An unlocking assembly push-in guiding assembly is arranged on the lateral side of the snap spring positioning assembly and comprises a triangular guiding piece matched with a long-strip-shaped groove of the unlocking assembly. During operation, the snap spring positioning assembly moves downwards to stretch into an upper sliding rail to position a snap spring, then the unlocking assembly push-in guiding assembly moves downwards, the triangular guiding piece is located between the upper sliding rail and the unlocking assembly push-in mechanism, and the unlocking assembly is pushed into the upper sliding rail through guiding of the triangular guiding piece.