Based on the hourly rainfall data, the frequency, rainfall and class-conditional probability density of day and night, winter and summer rainfall in different terrain ladder representative districts along the 30°N are statistically analyzed. The influence of different terrain heights with longitude on rainfall is explored by studying the distribution of day-night and winter-sumer ratios of rainfall. The results show that: (1) Along the 30°N, the rainfall and frequency ratio of night to day decreases eastward in the Sichuan Basin. Ya’an is the highvalue centre of strong night rainfall. The phenomenon of night rainfall tends to disappear to the east of 108°E mountain in the east of the Sichuan Basin. Night rainfall is more likely to occur in strong precipitation in the basin than in weak precipitation. (2) There is a big difference between winter and summer rains along the 30°N line. Winter rainfall is small, and summer rainfall is large; structurally, the rain is weak in winter and strong in summer; there are regional differences in frequency. The second topographic step has less winter and more summer rains, while the third topographic step in opposite. Winter rains is more obviously affected by large terrain. (3) According to the cluster analysis of the first kind of Class-Conditional Probability Density 1 (CCPD1) ratio of winter to summer and CCPD1 anomaly percentage of winter rains, the eight sub-regions can be divided into three categories, which have a good corresponding relationship with geographical location and terrain steps. (4) Summer rainfall is significantly affected by local terrain. The peak value area of anomaly percentage of the summer rain CCPD1 higher than 10% ( or valley of lower than -10%) is defined as the summer rain strong (weak) potential area, and the strong and weak potential areas are different. There is a great potential for short-term heavy precipitation in the south of Jianghan Plain and north of Poyang Lake, and there is a great potential for extreme short-term heavy precipitation in Ya’an (the strong potential area ≥ 61 mm). The strong potential area of winter rainfall (the peak area where the anomaly percentage of CCPD1 is higher than 50%) is located in divisions Ⅶ, Ⅷ and Ⅸ on the third topographic step (the potential value is 1 to 20 mm). Still, the precipitation range of 1 to 20 mm is a weak potential area (valley area where anomaly percentage of CCPD1 is lower than -50%) in Ya’an and the basin centre.