Based on the brightness temperature observed by the Fengyun-4A satellite, around eight hundred mesoscale convective systems (MCSs) are identified in the middle reaches of the Yangtze River Basin during the warm seasons (April–September) of 2018–2021, which are categorized into the quasistationary (QS) type and the outward-moving (OM; i.e., vacating the source region) type. Afterward, the initiations of the MCSs are backward tracked using a hybrid method of areal overlapping and optical flow. Then, the main features of QS and OM MCSs and their respective synoptic circulations and environmental parameters are analyzed. The QS MCSs primarily occur in July and August and are mainly initiated in the afternoon. The OM MCSs mostly occur in June and July with two initiation peaks appeared at noon and late night, respectively. The QS MCSs are mainly initiated in mountainous areas, and they are primarily caused by local thermal effects. In contrast, the OM MCSs are mainly initiated in plain areas under synoptic forcings. Circulations of a total of 285 days (without direct influencings from tropical cyclones) are objectively classified into three patterns by using the k-means algorithm. Pattern-I (128 days) which is closely related to low-level jets, shows the most similar features to those of typical Mei-yu fronts, and it acts as the most favorable circulation type for MCSs’ initiations. Pattern-II (66 days) is dominated by northwesterlies, with a relatively stable layer in the low-level troposphere. Pattern-III (91 days) features a dry-adiabatic or even a superadiabatic layer that contributes to lowering the layer stability.