Abstract: The cause of surface spot formation of cold rolled steel sheets were analyzed,the preventive measures of surface spot were studied by beans of quick wins and in-depth analysis method.The results show that the p H of liquid in wet flattening liquid system is maintained at greater than or equal to 7,less than or equal to 9,its concentration was maintained at more than 2.4%,less than or equal to 4%,can guarantee the product yield.If the mixing tank temperature in wet flattening liquid system was controlled in 50 ℃ above,the surface spots will be reduced.