Abstract: An analysis of the correlation between SARS cases from April 28^th 2003 to May 24^th 2003 and air pollution index in Beijing divided into three phases is carried out with approach of mathematical statistics. The study discovers a very high correlation between inhalable particulates and SARS cases, and SARS cases in Beijing show the best correlation with the air pollution index on the confirmed 4^th or 5^th previous day. It is not clear the mechanism that supports the phenomena. Suggestions for further study are put forward.