A cargo bed assembly for a pickup truck includes: a pair of side walls opposing each other; a truck bed located between the pair of sidewalls, and having a first cavity; a tailgate pivotally connected to a rear end of the truck bed by a first pivot pin, and having a second cavity; a slide unit movably received in the first cavity; and a step unit movably received in the second cavity. In particular, the second cavity is configured to communicate with the first cavity, and the step unit is pivotally connected to the slide unit.