Abstract: When coolant flows through the nuclear reactor core, the vast majority will go into fuel assemblies to take away the fission energy. Another small amount will go into the outer flow path of fuel assemblies as well as inner and outer flow path of control rod guide tube as bypass flow. To ensure the safety of nuclear reactor under normal operation condition, the flow rate of bypass flow must be limited. In this paper, an experiment was carried out to investigate the resistance characteristics of flow path outside guide tube. Pressure loss of different sections was obtained and the relationship between Reynolds number and resistance coefficient was fitted. Experimental results show that the pressure loss of flow path outside guide tube is mainly concentrated in lower plate. The bypass flow rate outside single guide tube is only 0.196 m³/h under normal operation condition.