During the loading process of the loading trolley, when the center line of the belt reel does not coincide with the axis line of the reel, it is easy to roll over, resulting in major personal and equipment safety accidents. In order to ensure the intrinsic safety of the trolley, this paper develops and designs a trolley safety device by using the analysis method of deductive reasoning and the principle that the rubber roller converts the translational motion into circular motion. The trolley is transformed and applied, which overcomes the influence of human negligence and the cumulative error of instrument measurement, and ensures the safety of the trolley. It has broad application prospects, At the same time, it also provides a useful reference for the safe operation of trolleys in similar production lines.