The invention discloses a dropping cocoon collecting device of an automatic silk reeling machine. The dropping cocoon collecting device comprises an inclined conveying belt and a collecting box. A plurality of criss-cross partition plates are arranged in the collecting box to form box cavities, and the partition plates, in the direction perpendicular to the conveying direction, in the collecting box are higher than the top of the edge of the collecting box. A horizontal collecting frame is arranged at the tail end of the conveying belt. An open water tank is arranged at the front end of the conveying belt, and a scraper driven by a stepping motor and a guide rail is arranged on the liquid surface of the water tank. Cocoon treating fluid is contained in the water tank. Compared with the prior art, the dropping cocoon collecting device can solve the problem that in an existing cocoon collecting device, cocoon separation is not convenient, and the follow-up process is influenced.