The invention discloses an automatic assembling device for an automobile seat sliding rail. The automatic assembling device for the automobile seat sliding rail comprises a sliding rail placing mechanism, a sliding rail core conveying mechanism, a ball and nylon rod loading mechanism and a base, wherein the sliding rail placing mechanism comprises two locating shafts and a sliding rail placing table; the sliding rail core conveying mechanism comprises two guide rails, a lead screw, a guide rail sliding block, a sliding rail core displacement table, a clamping device, a first servo motor and aguide rail support; and the ball and nylon rod loading mechanism comprises a loading frame, two stepped shafts, two stepped shaft supports, a nylon rod material frame, two ball material frames, a ballloading track, a nylon rod loading track and two second servo motors. The automatic assembling device disclosed by the invention has the advantages that all the parts cooperate, automatic assemblingof the automobile seat sliding rail is realized, labor cost is saved, time is shortened, efficiency is improved, and follow-up study on automobile seat sliding rail streamlined assembling can be carried out by utilizing the automatic assembling device disclosed by the invention.