The traditional method for calculating the ampacity of AC submarine cables does not consider the actual situation of the metal sheath circulation distribution during the operation. In response to this problem, this article proposes a calculation method for the ampacity of AC submarine cables that considers the sheath circulation. Taking a typical submarine cable HYJQF41-F-127/220 3×500 as an example, the finite element method is used to calculate the circulation and loss, simulate the heat distribution during the operation of the submarine cable, and calculate the ampacity. The results show that compared to the traditional method for calculating the ampacity, the results of this method are smaller, which is an important operating characteristic of AC submarine cables that is worth paying attention to by power grid operators.