The optical sensor is the core part of the optical partial discharge (PD) detection system in gas insulated switchgear (GIS). In this article, simulation and experiment studies are implemented for the design of optical PD sensors based on the light guide rod. Firstly, based on the TracePro simulation software, the front microstructure and length of the light guide rod are designed, and an optical sensor for GIS PD detection is proposed. Then, the GIS optical PD experimental platform is established to study the actual PD detection effects of different front microstructures and lengths. Both the simulation and experiment results show that the light guide rod with its front microstructure being concave cone shape and the length being as long as the inner wall of the tank has better detection effect. The consistence between the simulation and experiment results demonstrates the feasibility of the design and the correctness of the simulation model. Finally, several detection surfaces and detection points are set up in this simulation model, and the total irradiance maps of each detection surface and the light irradiance value of each detection point are observed and analyzed. The light irradiance values received by different detection points are related to component occlusion and the intensity of direct ray. Taking the y-115 PD source as an example, the light spots on the P1 detection surface are concentrated around 150° to 210°, while the optimal detection points on the P2 detection surface are mainly located around 30° and 330°. The research results provide some basis for the development of optical PD sensors in GIS.