The lowest-energy structures and the electronic properties of CdnSn(n=1-8) clusters have been studied by using density-functional theory simulating package DMol3 in the generalized gradient approximation (GGA). The ring-like structures are the lowest-energy configurations for n=2,3 and the three-dimensional spheroid configurations for n=4-8. The three-dimensional structures may be considered as being built from the Cd2S2 and Cd3S3 rings. Compared to the previous reports, we have found the more stable structures for CdnSn(n=7,8). Calculations show that the magic numbers of CdnSn(n=1-8) clusters are n=3 and 6. As cluster size increases, the properties of CdnSn clusters tend to bulk-like ones in binding energy per CdS unit and Mulliken atomic charge, obtained by comparing with the calculated results of the wurtzite and zinc blende CdS for the same simulating parameters.