An engineering approach on designing a hardware-in-the-loop simulation (HILS) platform for a UAV control system is introduced in the paper. Basing on a powerful real-time simulator and the multifunctional interface boards such as ADC, DAC Digital I/O and serial communication interface board, a HILS platform is constructed; in the HILS loop, there contain embedded control system, attitude sensors, actuator emulator system, turntable and dSPACE. HILS designing procedure is mentioned, as well as some practical problems to be noticed in the process of construction. Using NI (national instrument) PXI 104X series, we set up an actuator emulator system and testing system for the HILS system. The validation, verification and accreditation of the simulation result are discussed at the end of the paper.