The international maritime trade witnessed a rebound in 2021, with a growth of 3.2% compared to 2020, reaching a total shipment volume of 11 billion tons. Ports are a vital component of global maritime trade. To investigate the implications of increased trade volume on port workload and efficiency, a framework for analyzing ship traffic flow characteristics in ports is proposed based on Automatic Identification System (AIS) data. First, AIS data processing and analysis procedure is formulated. Then, the traffic flow characteristics of arriving ships, geometric distribution of arriving ships, and temporal patterns of arriving ships are analyzed. Taking Qinzhou Port in January 2021 as a case, it is found that medium-sized ships dominate the arriving ships, with an average port sojourn time 39.5% higher than other major container ports in China, indicating significant potential for improvement. This study also provides with data support for future simulations of ship traffic flow in ports.