A box cover of a pickup truck, includes at least two panels and at least one rotating shaft mechanism. The rotating shaft mechanism is connected with two adjacent panels, and the rotating shaft mechanism includes a base and two connecting units. The base includes a base portion having a hollow structure inside and two rotating shaft portions respectively disposed on two sides of the base portion. The base portion and one of the rotating shaft portion form a rotating space. The rotating space is isolated from the interior of the base portion. The connecting unit includes a fixing portion fixedly connecting with the panels and a rotary portion rotatably inserted into the rotating space. It is capable of avoiding water falling into the rotating space of the rotating shaft mechanism from seeping into the interior of the base portion of the rotating shaft mechanism. The structure is simple and waterproof.