Heavy rainstorms in the coastal region of South China are often caused by single warm air mass. Based on objective analysis by computational program, two types of convergence line, i.e. the southerly convergence line and southwesterly convergence line, are determined to be the major systems affecting the warm area heavy rainstorms. The structure of such convergence lines is characterized by a strong and deep warm center and ascending motions. The convergence line is essentially a strong synopticstorm system in warm air mass area. The southerly convergence line often occurs at the western coast of Guangdong Province of South China, which can induce short-term heavy precipitation clusters. The southwesterly convergence line often appears at the eastern coast of Guangdong and results in continuous heavy precipitation belts. Terrain in coastal region of South China is complex with various mountains and estuaries. Mountain Yunwu at the western coast of Guangdong can block the southerly convergence line at a right angle, while Mountain Lianhua at the eastern coast of Guangdong curves laterally to meet the southwesterly convergence line and imposes significant frictional effects on it. The numerical model WRF3.5 is applied to investigate the influence of mountainous terrain on the two types of convergence line with a focus on the effects of blocking at the right angle and the lateral friction. The results show that after the height of Mountain Yunwu is reduced by 80%, the southerly convergence line and the accompanied rainstorm move northward without the mountain blocking. Rainfall pattern and location also change, and the intensity decreases. The mountain blocking forces the low convergence flow to rise fast and triggers heavy rainstorm, while the latent heat release caused by condensation strengthens the convergence line. The depth and intensity of the warm center and the ascending motion all intensify, which in turn increases precipitation. The experiment with the narrow valley between Mountain Yunwu and the Mountain Tianlu to its southeast filled shows that the tunneling effect of the valley can determine the rainfall location and intensity. Due to thejoint effects of the valley tunneling and the blocking of Mountain Yunwu, the storm happens frequently in the western coast of Guangdong. In the southwesterly convergence line experiment, a comparison between two kind of roughness coefficients of Mountain Lianhua surface were made. A remarkable difference of vertical velocity appeared; the result showed that the lateral friction of Mountain Lianhua can enhance southwesterly convergence line and its ascending motions. Due to the shape of mountain is the southwest wards, it leads southwester jet flowing along the mountain. They maintain the longer rainstorm duration and belt shape of rainfall location. Meanwhile, it can influence the rainstorm at west coast and the estuary to become narrow and slightly move southward. The influence of mountain terrain is different from the synoptic systems because mountain can cause local faster lifting and can make thick upwards motion. Especially there is plentiful moisture vapor along the coast, the moisture condenses and releases latent heat at high level, then it enhances convergence line systems. The process causes the rainstorm intensity in single warm airmass is larger than that of front rainfall in South China.