Abstract: Beam position monitor (BPM) is an important part of the beam measurement system. In this article, by introducing the coupling capacitance (plate-to-plate cross-talk) and the difference capacitance of two electrodes into the formula of the linear-cut BPM by difference over sum method, the reasons of the low sensitivity and the offset of the electrical center of the BPM were got. The relationship between geometry and electronics parameters by combining the formulas and the calculated results of the CST program were obtained. Finally, by considering the requirements of the CSNS-RCS and electronics, the optimized geometry and the electronics parameters of the BPM were got.