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The characteristics and mechanisms of typhoon rainstorms in the Tianmu Mountain area are researched in this paper based on the automatic weather station data and ERA5 analysis dataset from classification, rainfall distribution, weather system and topography conditions during the process. The results show that: (1) The rainfall in the Tianmu Mountain area has been more in the northeast and northwest parts and less in the south part as a whole, and concentrates in the north of East Tianmu Mountain and Western Zhejiang Tianchi. (2) When the upper-level trough is the northwest-southeast type, the cold air behind the trough invades from the northwest to the south side of the typhoon in a cyclonic manner. It encircles the centre of the typhoon in a semi-encircling shape, which makes the typhoon appear an obvious relative warm centre again. It is conducive to the excitation of cyclonic vorticity and the enhancement of rainfall. (3) For the Tianmu Mountain area, the most favourable condition for triggering convective weather is the weak cold air with an intensity of 2 ℃, which intrudes into the bottom of the warm and humid air along the topography and makes the warm and humid airflow rise. (4) Affected by the windward slope effect, when the northwest wind in Western Zhejiang Tianchi has the most obvious increase in precipitation. The topography of East Tianmu Mountain is the northeastsouthwest valley type. The main reasons for the increase in precipitation are the windward slope effect and narrow tube effect, and the convergence line forms in front of the mountain due to the flow around and rebound when the airflow meets the mountain. The northward-moving typhoon is easy to induce the rainfall centre in the north of the Tianmu Mountain area, while the westwardmoving typhoon rainfall centre is in the east of the Tianmu Mountain area.