The invention discloses a fixing device for a garden plant. The fixing device includes a first fixing shaft sleeve and a second fixing shaft sleeve which are mounted on the plant, the two ends of the first fixing sleeve are provided with a connection lug separately, a fixing support is mounted on the outer portion of each connection lug, each fixing support is provided with a locking steel wire, the other end of each locking steel wire is provided with a ground insertion rod, the ground insertion rods are inserted into soil, the locking steel wire at each side is provided more than one tightness adjusting mechanisms, the two ends of the second fixing shaft sleeve are provided with self-locking mechanisms, one end of each self-locking mechanism is fixedly connected with the second fixing shaft sleeve, and the other end of each self-locking mechanism is arranged on the corresponding locking steel wire. The fixing device for the garden plant is simple in structure and can achieve the automatic adjustment on the locking steel wires and the adjustment on the tightness degrees of the locking steel wires, the self-locking mechanisms are further arranged, it is ensured that the locking steel wires are in locking states all the time, each locking steel wire can be set to be bent at one end through the tightness adjusting mechanisms, multi-layer locking makes the fixing capacity and the locking capacity higher, and the device does not easily loose.