A typhoon transitioning to an extratropical cyclone and merging into the Northeast cold vortex is one of the main weather processes causing widespread heavy rainfall in northeastern China in summer.However, the evolution characteristics and mechanism of the thermal and dynamical structures of the typhoon and the Northeast cold vortex in this type of process are not well understood.This study applies the re-analysis data of the National Centers for Environmental Prediction (NCEP) to diagnose an event in which a typhoon transitions and merges into the Northeast cold vortex.The results show that the persistent cold air invasion from the Northeast cold vortex and the relative cold advection caused by the movement of the typhoon gradually destroyed the warm core of the typhoon.As a result, the low-level low-pressure convergence and upper-level high-pressure divergence associated with the warm core disappeared.After the typhoon transitioned and merged into the Northeast cold vortex, the entire troposphere became relatively cold, and a cold center formed at the low troposphere.As the typhoon transitioned to an extratropical cyclone and merged intothe Northeast cold vortex, the anti-cyclonic wind shear at the south side of the upper-level jet near the center of the Northeast cold vortex inhibited the vertical upward development of the cyclone.However, the features of thermal and dynamical distributions on the left side of the upper-level jet axis favored vertical vorticity development, and the maintenance of the tilted upper-level jet axis caused by the cyclone approaching the Northeast cold vortex enhanced the slantwise upward development of the cyclone.Moreover, the vertical vorticity at the middle troposphere of the cyclone increased rapidly due to the slantwise lifting of low-level air along the tilting pseudo-equivalent potential temperature isolines from the east side of the cyclone.The tilting of pseudo-equivalent potential temperature isolines were caused by the cold air packing near the low levels of the cyclone.After the typhoon transitioned and merged into the Northeast cold vortex, a distinct positive vertical vorticity advection from the upper-level cold vortex bottom prompted the vertical upward development of the cyclone.The eastward movement of the jet at the upper-level cold vortex bottom was favorable for maintaining the positive vertical vorticity advection.The vertically upward development of the cyclonic circulation weakened the upper-level circulation of the Northeast cold vortex, leading to its northward retreat.