Abstract: By using NCEP global 1°×1° re-analysis data,real-time radiosonde and intensive surface observation data,a comprehensive analysis was made of the influence of circulation background,underlying surface and cold air activity on the track and precipitation change of typhoon “Rananim” after landfall.At the same time,a diagnostic analysis was also conducted through computing the distribution of physical quantities.The results show that(1) the change of typhoon “Rananim” track from north-west to west after landfall is mainly due to the zonality of 500 hPa subtropical high,the increasing east wind near the north side of the typhoon and the sharply enhanced wind difference of absolute u component between the north and south sides before landing;(2) the intruding of cold air results in the track of the typhoon moving towards west-south during its final stage,which can be represented by the wind difference of absolute v component between the east and west sides of the typhoon,in addition,cold air is helpful for maintaining the typhoon depression circulation in the first stage,and filling it up in the final stage;(3) the ascending velocity,divergence and moisture flux all contribute to the heavy precipitation over the area of Boyang Lake when “Rananim” is moving westwards through this area,which is highly correlated to the exchange of heat and water vapor on the water surface of the lake.