The invention relates to a fixing device capable of being attached with maritime plants. The fixing device comprises a supporting part, a containing space, a bearing part, a containing unit and an adjusting unit, wherein the supporting part is provided with an open end part and a closed end part and connected between the open end part and the closed end part; the containing space is defined by matching the open end part, the closed end part and the supporting part; the bearing part is arranged in the open end part; the containing unit is movably arranged at a blocking part of the open end part; the adjusting unit is movably arranged at the bearing part; the containing space is divided into a first section near the open end part and a second section near the closed end part by the bearing part; the supporting part is provided with at least one opening communicated with the second section; the adjusting unit is positioned in the first section; one of the adjusting unit and the closed end part is provided with at least one locating hole, and the other one is provided with at least two locating holes; when the blocking part is positioned at a first position, the adjusting unit can freely rotate relatively to the bearing part; and when the blocking part is position at a second position, the blocking part can limit the rotation of the adjusting unit.