Abstract: The distribution of CH,background concentration in the troposphere and the characteristics of it's variation with latitude,season and elevation were discussed at sampling range of 30-450N,88-1380E in China during the period July 1988 to May 1990.The values of CH9 concentration decreased as the altitude increased,and increased as the latitude increased.Through measurement of air samples collected weekly,it is found that there was significant seasonal variation at the Lu Shan mountain and Wutai Shan mountain in April 1989 to May 1990.The lower values appeared in the Summer.The higher values arose in the end of spring and early autumn.By using samples collected in the aeroplane,a vertical gradient was observed between earth's surface and the height of 4000 metres (m) over Gubantiinggiit desert at Xinjiang in November 1989.