In order to improve the understanding of the characteristics and mechanisms of typhoon remote rainstorms within the subtropical high, a remote rainstorm process triggered by Typhoon Mangosteen in 2018 is analysed using multi-source observation and ERA5 reanalysis data. The results show that: (1) The rainstorm occurred within a strong convective and unstable environment characterised by high temperature, high humidity, and high energy within the 500 hPa subtropical high. The rainstorm area was located at the north end of the typhoon trough at the lower level, within the southerly wind speed convergence area, and to the right side of the upper jet stream inlet area. (2) The lower-level warm and humid advection provided sufficient water vapour and energy, promoting the development and maintenance of convective unstable stratification. Strong upper-level divergence coupled with lower-level convergence induced a strong upward motion, which provided favourable dynamic conditions for the rainstorm. (3) The mesoscale convective system exhibited three evolution stages: the organisation and establishment of banded convection, the development and movement of supercells in the south, the weakening of convection in the north, and the development of new convection in the south, resulting in extreme short-term heavy precipitation (exceeding 100 mm/h) during two stages. (4) The low-level North China high combined with the typhoon trough and the offshore high successively enhanced the low-level convergence and maintained the shear line (surface convergence line), which was conducive to the development and maintenance of convection. The typhoon trough acted as the trigger and organiser of the initial convective zone, and the outflow of the thunderstorm cold pool played a pivotal role in the development and movement of supercells. (5) The divergence and suction force of the upper jet stream in the mid-level convergence, the development of positive vorticity and low trough, and the enhancement of vertical wind shear in the rainstorm area were conducive to the development of the southern convective zone. During typhoon activity at the low latitudes, there was a typhoon trough at the lower level of the 500 hPa subtropical high, and the convergence area at the northern end of the typhoon trough was the focus of long-range rainstorm forecasts.