The TRMM data, conventional observation data, NCAR/NCEP2 reanalysis data and global data assimilation system (GDAS) data are taken to investigate the strong enhancement of tropical cyclone rainstorm when tropical cyclone accompanied with South China Sea monsoon trough lands in South China. Based on the observational facts, the event that the tropical cyclone accompanied with a monsoon trough la nds in South China is defined. The results show that strong enhancement of tropi cal cyclone rainstorm usually happened in July to September. The synopticclima tic characteristics are that subtropical high intensifies zonal spreading wester ly and dominates over middle China. Meanwhile, South China Sea monsoon is in its active period, South China Sea monsoon trough locates over north of South China Sea. The lifetime of tropical cyclone after its landing is prolonged due to the accompanying South China Sea monsoon trough. Cloud system of tropical cyclone has a process of regeneration, strengthening and spreading. Tropical cyclone rai nstorm gains strong increment on rainfall intensity and tropical cyclone lifetim e. The rainfall area stretches on the south of the monsoon trough about 1500～25 00km.