The present invention discloses a method and an apparatus for acquiring a current to ground of an ultra high voltage cable line. The method comprises: acquiring a length of a cable line between two adjacent towers in a power transmission and transformation system, a cable parameter, a voltage and a capacity of a main transformer at an input end of the power transmission and transformation system, and an electrical load of a user at an output end of the power transmission and transformation system; according to the length of the cable line and the cable parameter, establishing a cable model corresponding to the cable line by using ATP_LCC software; according to the voltage and the capacity of the main transformer, acquiring a main transformer model corresponding to the main transformer in ATPDraw software; according to the electrical load of the user, acquiring a user model corresponding to the user in the ATPDraw software; and according to the cable model, the main transformer model and the user model, performing digital simulation on a transient fault of the power transmission and transformation system during a running process to obtain a current to ground of the cable line. According to the method and the apparatus for acquiring the current to ground of the ultra high voltage cable line provided by the present invention, a technical problem of failing to accurately acquire the current to ground of an ultra high voltage power transmission system in the related art is solved.