Abstract: Provided is a freight loading system of a trailer including: a loading container having a loading section in which freight is loaded; a conveyor installed at the loading section, and conveying the freight into the loading container using a drive motor; a palette on which the freight is loaded to be conveyed by the conveyor; a palette up/down cylinder installed at the loading section; a palette lifting member for lifting the loading palette over the conveyor using the palette up/down cylinder; a palette fixing part for fixing the loading palette lifted over the conveyor by the palette lifting member; a freight fixing cylinder for pressing and fixing the freight loaded on the loading palette; and a pressure supply apparatus for supplying hydraulic or pneumatic pressure to operate the palette up/down cylinder and the freight fixing cylinder.