Water cooled chillers are widely used in air conditioning systems. The value of COP (Coefficient of Performance) is a key performance parameter for chillers, and it is different under different working conditions. It is desirable to get its performance under standard condition for comparison and assessment. In this paper, a way to convert in-situ testing results to standard condition is put forward. This is called normalization. A method of COP normalization of in-situ testing of water-cooled chillers for air-conditioning is put forward and discussed in this paper, and the following conclusions are obtained: 1) The COP within the permitted error under standard condition can be obtained from in-situ testing data of water-cooled chiller under various in-situ conditions. The normalization method is rational. 2) The normalization error is sensitive to entering condenser water temperature. When the entering condenser water temperature is not close to standard condition, the error is relatively large. 3) The error is not sensitive to the leaving evaporator temperature. When evaporator water temperature difference between in-situ testing and standard condition is large, the error is small if the condenser temperature is close to standard condition.