According to the test needs of the off-axis control system of the IR air-to-air missile launcher, aiming at the problems that the previous testing equipment failed to simulate the seeker following targets in real-time, and the analog circuits with complex debug and difficult check-up. By analyzing the working process of the missile's off-axis control loop and the control algorithm of valves, the paper proposed the design basis on DSP, using the basic digital and analog integrated circuits, and software programming, which simplified the off-axis control circuit of the previous testing equipment, and implemented the function of simulating the seeker following targets in real-time. Its correctness is fully validated in the products.