The relationships between the results of Beijing International Marathon Races and the corresponding weather conditions are analysed quantitatively. There are obvious interrelationships between the marathon results and weather factors such as air temperature, wet bulb temperature and human biometeorological indices. For example, the correlation coefficient between the average times of the top ten finishers and temperature isr=0.8910. The meteorological conditions are classified into three categories, suitable, moderate and unsuitable for running a marathon race, and the optimum meteorological index is given. Also the concept of a meteorological result, i.e. the part of the actual performances fluctuating with the changes in weather conditions, is presented. This plays an important role in some kinds of sports such as marathon racing. Finally, the results of physiological tests are given, which illustrate the physiological reactions of long- and middle-distance runners to the surrounding temperature.