The invention provides a trailer bottom plate heating device. The device involves a main vehicle and a trailer which is dragged by the main vehicle, wherein the trailer is provided with a frame and acarriage carried on the frame, an annular frame air inlet groove is formed on the frame, the diameter of the frame air inlet groove is larger than the width of the frame, the frame air inlet groove isprovided with one or more groove hole parts and an annular groove, the groove hole parts are vertically arranged and are provided with upper openings and lower openings, and the annular groove communicates with the lower openings; and tail gas discharged by the main vehicle enters the groove hole parts from the lower openings of the groove hole parts through the annular groove, and is dischargedfrom the upper openings into a tail gas flowing space arranged on a carriage bottom plate, so that the tail gas flows in the range from the foremost end to the rearmost end of the bottom plate in theheading direction of the trailer, and from one side end part to the other side end part of the bottom plate in the width direction. According to the device, the problems that the unloading difficultyis large and unloading is incomplete due to the fact that cargoes are frozen to attached on the carriage can be solved by utilizing the waste heat of the tail gas in a cold region, and the transportation efficiency is improved.