External well slots technology can meet the demand of increasing well slots on existing platforms economically and effectively, but the implementation of external well slots scheme is affected by many factors, among which the bearing capacity of the pile foundation is one of the important factors affecting the feasibility of the external well slots scheme. Taken a 4-leg platform of Bohai oilfield as an example, the influence of the external well slots on the bearing capacity of the pile foundation is divided into three aspects. The influence of the changes of the horizontal load, vertical load and position of workover rig on the pile head force caused by the external well slots is mainly analyzed. The change rules of the platform pile head force are summarized by comparing the pile head force before and after platform external well slots modification. According to the rules, the change of pile head force is estimated. The error of the prediction results is very small, which can be used as the basis for judging whether pile legs need to be added in the scheme of external well slots in the preliminary research scheme design stage.