Abstract: An analysis on the seasonal features of epidemic cerebrospinal meningitis during 1975-1995 by using cosine model was carried out in Henan province.The results showed that after the inoculation group A menigococcal polysaccharid vaccine,the incidence rate of this disease was decreased to a lower level,epidemic period was delayed to January-May,the patients were disperse in the whole county.There was no significant variation of seasonal peak,it was still in March.The authors suggested that it was neccssary to completed the in-oculation group A menigococcal polysaccharid vaccine in the first tem days of December in ev-ery year.The significance of the Cosine model in the analysis of the difference in epidemic peak period was discussed.