A carrying device and a folding method thereof are disclosed. The carrying device includes a seat assembly, a front-leg assembly and a rear-leg assembly. The front-leg assembly includes an upper frame, a lower frame, a first transmission member and a second transmission member. The upper frame is disposed at the lower frame. The first transmission member is disposed at the upper frame and corresponded to the second transmission member. The rear-leg assembly disposed at the lower frame includes a third transmission member disposed corresponding to the second transmission member, a rear-leg frame, and a connector connecting the rear-leg frame with the lower frame. When the upper frame moves relative to the lower frame, the first transmission member drives the third transmission member to move by the second transmission member to link the connector to make the rear-leg frame approach or move away from the lower frame.