cases of prehospital sudden death patients who received prehospital emergency medical care provided by the Shanghai Medical Emergency Center from January to December in 1999 are collected. The seansonality of Prehospital sudden death and its relationship between weather and climate are analyzed in order to decrease the sudden death related to weather change. The results show that 70.44% of the patients had a history of diseases before sudden death, high sudden death incidence happens in the age group of 60-80 years old that account for 64.48% of all patients. The male patients are more than the females. The incidence rate of prehospital sudden death patient is the highest in winter and the peak happens at 07:00 am in a day. There is a positive relationship between the total of sudden death and the variation of relative humidity and mean air pressure,and a negative relationship with minimum temperature and mean temperature. The cardiovascular-related sudden death, beside the above factors,is a positive relationship with the changes of the air pressure, the minimum temperature,and the radiation hours etc. Also, there is a negative relationship between coronary heart disease, other heart disease and mean wind velocity, and there is a positive relationship between hypertension and mean air pressure.