A waterproof decorative lamp includes an illuminating body having a first end, a second end opposite the first end, and an outer wall extending between the first end and the second end, a plurality of wires connected to the first end of the illuminating body, an isolation fixing column clamped between the plurality of wires, and a housing coupled to the isolation fixing column, the housing having an inner wall defining an inner cavity. The housing is installed from the second end of the illuminating body, the housing sheaths a periphery of the isolation fixing column and a periphery of first end of the illuminating body close to the wires, the second end of the illuminating body is exposed from the housing, the inner wall of the housing abuts against the outer wall of the illuminating body, and the wires are clamped between the isolation fixing column and the inner wall.