Abstract: Typhoon "Maysak" (2009) was formed of the East ocean in the Philippines, then moved north along the coastal waters of China and continued to strengthen, reaching a super typhoon at its strongest. After landfall, the typhoon moved westward in the Northeast of China. The combination of the typhoon and the cold vortex gradually strengthened and moved slowly, bringing a large range of continuous heavy rain to the central and northern parts of the northeast. Based on FY-2F infrared brightness temperature data, the conventional observational data and NCEP FNL reanalysis data, the weather process of typhoon "Maysak" degeneration intensification due to its combination with cold vortexes when it went deep inland in mid-high latitude westbound was analyzed. The major conclusions are as follow: (1) the favorable high and low air dynamic condition configuration and the phase change driving action of water vapor led to the asymmetric development of typhoon, which presented a west-inclined structure in the vertical direction. The main cloud system and heavy precipitation mainly appeared on the left side along the shear direction. (2) Typhoon rainstorms were dominated by stable precipitation, and only the short-time heavy precipitation caused by convective activity appears at the beginning of the precipitation. The mesoscale strong frontal zone in the lower layer of the front was a good indicator of the rainstorm. (3) Typhoon carried abundant water vapor northward, and the specific humidity in the middle and lower layers of the southeast heavy rain region was larger. The heavy precipitation was concentrated in the period of time and the precipitation intensity was high. The convective instability and wet symmetry instability in the middle layer of the warm front are conducive to the maintenance and development of heavy precipitation in the southeast heavy rain region. During the process of typhoon going deep into the inland, it developed variously, moved slowly, and the precipitation lasted for a long time, which was dominated by the stable precipitation of front and cyclone. (4) The rainstorm zone in the southeast was located on the north side of the Changbai Mountains. The easterly low level jet was orthogonal to the topography, and the windward slope topography increased the precipitation. The trend of the rainstorm zone was consistent with the topography.