An electrostatic measuring method for an inner wall of a fluid pipeline includes a step of disposing a grounded metal plate to an outer wall of the fluid pipeline; a step of forming a grounding effect through the grounded metal plate and the outer wall, wherein the grounded metal plate has induced charges, the induced charges combine outer-wall existing charges on the outer wall to form total outer-wall charges, and the total outer-wall charges are related to charges to be measured on the inner wall of the fluid pipeline; and, a step of measuring an electrostatic voltage above the grounded metal plate so as to obtain the charges to be measured on the inner wall of the fluid pipeline. In addition, an electrostatic measuring system for inner wall of fluid pipeline is also provided.