The present disclosure relates to a method and system for adjusting a focal point position of an X-ray tube. The method may include: obtaining a first thermal capacity and a first position of a focal point of an X-ray tube; obtaining a second thermal capacity of the X-ray tube; determining a second position of the focal point the X-ray tube based on the second thermal capacity; determining a target grid voltage difference of a focusing cup of the X-ray tube based on the first position and the second position of the focal point; and adjusting the X-ray tube based on the target grid voltage difference.