The article introduced one method of GC/MS and GC to determine the Daconil in pool water. The method is a simple, rapid, high sensitive and accurate solution. The minimum detection amount of Daconil is around 0.2ug. Daconil is a bit sensible to fish. Currently, some criminals pot it into pool to poison fish. There are several cases like this in our province. We detected pool water by GC/MS and GC and achieved a correct conclusion. Daconil is detected in pool water.