Based on satellite data, observational data, L-band second-level radiosonde data, and NCEP/NCAR 1°×1° reanalysis data from 2005 to 2017, the synoptic patterns of mesoscale convective complex (MCC) over the middle reaches of the Yellow River are classified, and their structural characteristics are comparatively analyzed by synoptic and dynamic diagnostic analysis. The results are listed as below. 1) In the middle reaches of the Yellow River, MCCs are mainly generated in the summer and generally develop to be mature from dusk till dawn with a long life cycle and slow movements. MCCs mainly produce rainstorm or above-level precipitation with high intensity and significant regional distribution differences. 2) According to the circulation at 200 hPa, the synoptic situation of MCCs are classified into three main patterns, and each main pattern is classified into different secondary patterns according to the circulation at 500 hPa. By comparative analysis of the structural characteristics, environmental conditions, and physical parameters of different MCCs patterns, the key forecasting techniques of heavy MCC precipitation are summarized and the physical models of MCCs are set up. 3) MCCs occur near the positive center of specific humidity and energy disturbance at the lower layer and develop to be mature at areas of great disturbance gradient near the positive center. The development of MCCs and the precipitation intensity have close relationships with the height, intensity, and thickness of the positive disturbance. 4) Though cloud system and vertical variations of ambient atmosphere display obvious differences in different life stages of different MCC patterns, the descent of cloud top, the thickening of moisture level, the decrease of condensation level, and the disappearance of inversion layer are premonitory signals of MCCs developing to be mature. 5) Under the background of stable South Asia high at 200 hPa，there are subsynoptic-scale cold front, mesoscale high, and cold pool on the surface. The impact of mesoscale high is less than that of cold pool, whose intensity and duration are closely related to intensity and duration of MCC precipitation. While under the background of thick upper trough and northwestern jet stream or jet stream branch at 200 hPa, there are no cold pool and mesoscale high on the surface. The increase of inflow wind speed and temperature gradient at the lower layer are the main factors for MCCs developing to be mature. The triggering mechanism of mesoscale dew-point front on heavy MCC precipitation cannot be ignored.