The invention discloses an automatic assembling device for an inner cap body and an outer cap body of a bottle cap. The automatic assembling device comprises an operating table mechanism, an outer cap body gluing mechanism, an inner cap body rotating mechanism and a pushing mechanism; the operating table mechanism comprises a rack, a panel with a slider storing groove, inner cap body orientation clamps, a thrust cylinder group and a slider group; the thrust cylinder group consists of a plurality of thrust cylinders; the slider group consists of a plurality of sliders; the panel is fixed on the rack; the slider group is arranged in the slider storing groove; each slider is provided with an outer cap body storing groove and the corresponding inner cap body orientation clamp; the four thrust cylinders are respectively arranged at the edges of four sides of the square panel and correspond to the sliders of the slider group exactly; the outer cap body gluing mechanism comprises a gluing support, an outer cap body lifting cylinder group, a swinging motor group and a gluing nozzle; each swinging motor is fixed on the corresponding outer cap body lifting cylinder; and the outer cap body lifting cylinders are fixed on the gluing support. By the automatic assembling device, the inner cap body and the outer cap body of the bottle cap can be assembled automatically.