Abstract: This paper aims to further understand the causes of the north-west line typhoon and provide a reference for its forecast. Based on 1°×1° NCEP reanalysis data, satellite infrared cloud image data, and real-time positioning typhoon intensity data, the intensity, track characteristics and causes of typhoon “Kalmaegi” were analyzed. The results showed that “Kalmaegi” was driven by subtropical high’s peripheral airflow, different phases were influenced by the steering flow from different levels. The greater the steering flow was, the faster the typhoon moved. In addition, the intensity changes of the steering current might also be an important reason for the typhoon path swing. The downstream of “Kalmaegi” with weak vertical wind shear zone, the involving of southwest monsoon and the cross-equatorial flow, and the asymmetrical distribution of wind field were reasons for intensified “Kalmaegi”. The study also showed that sensible heat and latent heat played different roles in different phases. In addition, this paper further analyzed the possible reasons for the strength of “Kalmaegi” remaining at typhoon grade at the mature stage.