Abstract: Based on multisource observational data and ERA5 reanalysis data, the differences of mesoscale convective systems (MCSs) were analyzed during heavy rainfall in eastern Gansu Province from 15 to 16 July 2022. The results show that: (1) This process was successively caused by the quasi-stationary MCS-A affecting from southern Ningxia to northern Shaanxi, MCS-B affecting most of southeast Gansu, MCS-C developing locally in eastern Longdong, Gansu, and broken line MCS-D forming in western Shaanxi, resulting in four rainbands. (2) MCS-A occurred during the precipitation stage 0000–1200 BJT (Beijing time) 15 July in the warm region; its rainband 1 had a small range, considerable cumulative rainfall, strong convection, and stable changes, with extreme heavy rain occurring locally, making it the strongest process. The other three MCSs occurred in the baroclinic frontal precipitation stage (1300 BJT 15 July to 0200 BJT 16 July). Rainbands 2, 3, and 4 occurred in the stages of MCS-B triggering, MCS-B merging with MCS-C to form a squall line, and the squall line fracture merging with MCS-D and strengthening again, respectively. Rainbands 3 and 4 exhibited higher precipitation intensity, whereas rainband 2 was weaker. (3) The cloud top structure of MCS-A is characterized by a quasi-oval cloud developed in isolation, with a back-building convection structure at the middle and lower levels, indicating a significant train effect. The cloud top structure reflects a banded mesoscale sustained stretching-type convective system formed from MCS-B, MCS-C, and MCS-D, with their mesoscale and lower convective structures showing a trailing stratiform pattern. (4) During the development of MCS-A, two persistent ground-based cold pools interacted. The initiation of MCS-A is linked to the outflow boundary from the downstream cold pool 2, as well as the convergence, mesoscale frontogenesis, and subtle temperature and humidity perturbations induced by the blocking effect of upstream cold pool 1. Subsequently, this system is sustained over an extended period through a phase equilibrium between the cold pool and lower-level vertical wind shear, fluctuations in low-level jet stream wind velocity, and the mutual cancellation of advection and propagation. (5) MCS-B was initiated by a 700-hPa shear line. Subsequently, as various types of surface convergence lines merged into a “three point” amidst intensified temperature and moisture disturbances, MCS-C and MCS-D were successively triggered. Their sustenance can be attributed to recurrent mergers, strong water vapor transport at mid-to-low levels, and the generation of cold air at mid-to-upper levels.