A device for evaluating a scale inhibitor for a circulating cooling water system, the device including: an open vessel, the open vessel including a first fixing hole, a second fixing hole, and at least one test hole; a stirrer; a test piece; a condenser; and a constant temperature heater. The open vessel is disposed inside the constant temperature heater. The first fixing hole is used to fix the stirrer. The second fixing hole is used to fix the condenser. The test hole is used to fix the test piece.