A new evaluation method of the aquiculture loss caused by red tides has been discussed in the present study. By analysing the structure of loss caused by red tide hazard, the aquaculture loss is divided into three types: direct aquaculture loss, indirect aquaculture loss and recovery cost. In addition, based on the different demand of timing, it was also divided into three grades: prediction assessment before hazard, tracking or monitoring assessment during hazard and onthespot surveying assessment after hazard. Finally, a practical example of assessing the loss of red tides occurring in Nanji Island, Zhejiang in June 2005, was given by red tides hazard loss assessment system established above. Its results were as follows: Prediction assessment before hazard: Classification is BR2. Early warning color is orange, and the second emergency measure was taken. Tracking or monitoring assessment during hazard: the direct economic loss is RMB 33 million. Onthespot surveying assessment after hazard: the direct economic loss is 31 million. The total economic loss is 42.9 million.