Mesoscale convective systems (MCSs) are classifi ed and investigated through a statistical analysis of composite radar refl ectivity data and station observations during June and July 2010-2012. The number of linear-mode MCSs is slightly larger than the number of nonlinear-mode MCSs. Eight types of linear-mode MCSs are identifi ed: trailing stratiform MCSs (TS), leading stratiform MCSs (LS), training line/adjoining stratiform MCSs (TL/AS), back-building/quasi-stationary MCSs (BB), parallel stratiform MCSs (PS), bro-ken line MCSs (BL), embedded line MCSs (EL), and long line MCSs (LL). Six of these types have been identifi ed in previous studies, but EL and LL MCSs are described for the fi rst time by this study. TS, LS, PS, and BL MCSs are all moving systems, while TL/AS, BB, EL, and LL MCSs are quasi-stationary. The average duration of linear-mode MCSs is more than 7 h. TL/AS and TS MCSs typically have the longest durations. Linear-mode MCSs often develop close to the Yangtze River, especially over low-lying areas and river valleys. The diurnal cycle of MCS initiation over the Yangtze River valley contains multiple peaks. The vertical distribution of environmental wind is decomposed into storm-relative perpendicular and parallel wind components. The environmental wind fi eld is a key factor in determining the organizational mode of a linear-mode MCS.