The corrosive nature of corrosion and scale inhibitor for circulating cooling water of the coal-fired power plant were evaluated through rotary coupon and electrochemical tests with concentration ratio of 2. 5 and 3 times. The results showed that it only inhibited the carbon steel corrosion when inhibit addition was greater than or equal to 10 mg / L. The results of the electrochemical test were consistent with the rotary coupon test.