In this paper, the main characteristics of the 6th typhoon In-fa in 2021 and the difficulties in the major adjustment process of typhoon track forecast are analyzed and studied. The main conclusions are as follows. (1) Typhoon In-Fa moves slowly and it is the first typhoon to land twice in Zhejiang Province, lingering for a long time near the northern Zhejiang and Hangzhou Bay. (2) The rainfall affects a wide range with large accumulative precipitation and long duration of strong wind. (3) The important and difficult problems reflected are as follows. It is difficult for forecasters to make corrections when there are consistent deviations in most model forecasts. Therefore, it is necessary to carry out the forecast verification work for the systems, such as upper-air cold vortex and tropical upper-tropospheric trough, which have important influence on the typhoon in the models. The slow movement of the typhoon is difficult to quantify, so it is necessary to carry out a quantitative study on the influence of the typhoon in the east on the slow movement of the typhoon in the west by summarizing historical cases and sensitivity tests. It is difficult to quantify the influence of the westerly trough/ridge on the retreat/advance speed of the subtropical high, which affects the forecast of the turning point of northward typhoon, especially when different models have divergent forecasts.