Runtime power and thermal management has attracted substantial interests in multi-core distributed embedded systems. Fast performance evaluation is an essential step in the research of distributed power and thermal management. Compared to software simulation, an FPGA-based evaluation platform provides fast emulation speed which enables us to test the performance of power/thermal management policies with real-life applications and OS. Compared to computer clusters, an FPGA-based platform has the flexibility to be configured into any network topology and hardware sniffer for performance monitoring can be added easily. This paper presents an FPGA based emulator of multi-core distributed embedded system designed to support the research in runtime power/thermal management. The system consists of multiple FPGAs connecting through Ethernet with each FPGA configured as a multi-core system. Hardware and software supports are provided to carry out basic power/thermal management actions including inter-core or inter-FPGA communications, runtime temperature monitoring and dynamic frequency scaling.