Earthquake sequences in which mag nitude of main shock is over 4.9 since 1965 in Yunnan area are selected. According to spatial distribution of early aftershocks of 51 earthquake sequences, data of source rupture length are obtained. The empirical relationships between magnitude and source rupture length are calculated by least squares linear regression model. The results of this paper is useful to analyze seismic hazard in Yunnan where shallow-focus earthquakes often take place.