•Design of Electric Core Simulator System for large sodium facility is described.•Using equivalent property concept, the Peak Cladding Temperature (PCT) characteristic was conserved within reasonable range.•Thermal-fluidic behavior (heat transfer and pressure drop) was conserved. The second phase of STELLA program (STELLA-2) has been started to verify and validate the performance of DHRS of PGSFR, and the construction of the facility is expected to be completed in 2019. The STELLA-2 is not only aimed for investigation of decay heat removal characteristics but also demonstrates its performance while interacting with PHTS of pool-type design. For comprehensive understanding of the phenomena, all systems and components of significance in the reactor need to be modeled as closely as possible and the core is one of such significant areas to be taken into account. To simulate the thermal-fluidic behavior and to observe the Peak Cladding Temperature (PCT) phenomena in core, the Electric Core Simulator System (ECSS) has been designed through similarity consideration by the scaling analysis with conservation of dimensionless number groups under the global/local scaling law. In this paper, the design consideration and process of the electric heater rod and the ECSS is described. The equivalent property concept was introduced and the thermal-fluidic behavior in PHTS pool was also conserved. Finally, the ECSS design was evaluated by MARS-LMR code and the comparison result between reactor core and that of ECSS in STELLA-2 is also described.