The reason why it is the resistor array but not the Digital Micro-mirror Device(DMD) that the widely used infrared scene projector was based on real time hardware-in-the-loop simulations(HILS) was pointed out. It was found that both image data transmission bandwidth of the interface and latency of external synchronization signal had impact on real-time performance. Analysis proved that only when the image data transfer bandwidth was 2 times higher than the effective bandwidth, it will meet the critical requirement of real-time simulation system. Dedicated Gigabit Ethernet hardware which meets this requirement was designed, and its software was compliant with UDP/IP protocol. The image transfer delay was only last for one MAC frame. The image data was reordered and stored in a particular way. Experiments proved that with great stability the speed of transferring 8-bit image data with 1 024×768 resolutions was above 100 Hz and the latency between external synchronization signal and starting signal of projecting was only 70 μs.