The goal of this paper is to describe the development of a hardware-in-the-loop simulation and verification environment for Field Programmable Gate Array (FPGA) based on-board computing systems. The underlying simulation environment is the Model-based Development and Verification Environment (MDVE). MDVE is an infrastructure for model-based engineering developed by EADS Astrium. A simulation environment based on MDVE was developed at the Universität Stuttgart. Recently, the demand on applying new high density FPGA technologies for innovative spacecraft on-board computing systems is rising. The small satellite "Flying Laptop" which is built by the Universität Stuttgart is the demonstrator of a FPGA-based on-board computer. In order to develop and verify the hardware and control algorithm of the computer, an extended simulation interface between MDVE and FPGA-based computing systems is established. This environment is capable of software verification and real-time simulation/verification configuration, and enables not only on-board software development but also functional real-time hardware evaluation of all the satellite components under precise space environment models. This paper describes the detailed implementation of this simulation interface and illustrates the obtained simulation results on attitude control algorithm verification and power budget calculation as well as communication timing analysis, which ensure the validity of the implementation.