Fault currents distributed on optical composite overhead grounding wire (OPGW) have a significant influence on the safe operation of the overhead transmission system. Traditional calculation methods include simplified calculation method and sequence component method. These two only focus on the grounding fault at one of the power towers. Owing to much ignorance, the calculation results are too simplified and not reliable. To solve these problems, this paper discusses the calculation of the grounding fault current distributed on OPGW at any point of the transmission line based on phase component method. The whole line can be divided into different sections by each power tower. Separately, two mathematic modulations are built when the grounding fault at tower and between towers. Numerical examples are applied to verify the correctness of theories of fault at the tower, and then the results are used to verify the correctness of fault between towers, finally applied into an actual project. In the complex overhead transmission system with OPGWs, phase component method proposed can accurately calculate the current distribution with grounding fault at any point of the line.