A canopy assembly includes a canopy fabric, a plurality of tightening wires, and a fastening arrangement. The fastening arrangement includes a plurality of tension adjustment units. Each of the tension adjustment units includes a supporting frame, a ratchet gear, a main shaft connected to the ratchet gear and rotatably connected to the supporting frame, and a resilient locking member mounted on the supporting frame to move between a locked position and an unlocked position. In the locked position, the resilient locking member is pivotally moved to engage with the ratchet gear so as to limit the ratchet gear to incrementally rotate in one predetermined direction with respect to the supporting frame, When the resilient locking member is in the unlocked position, the resilient locking member is pivotally moved to disengage from the ratchet gear so as to allow the ratchet gear to freely rotate with respect to the supporting frame.