Even-order aspheric surfaces are usually used to improve system performance when designing infrared systems. The optimization function of the design software can quickly find the best aspheric surfaces, but these aspheric surfaces are likely to have oscillating surface patterns. In order to eliminate the irregular aspheric surfaces in the infrared imaging lens and reduce the narcissus phenomenon of the system, the evaluation parameters of the narcissus phenomenon are first analyzed from the definition perspective. Combined with the narcissus light trace diagram, it is determined that the narcissus evaluation parameters are still suitable for the narcissus control of the aspheric surfaces. From the perspective of the sagittal height, the monotonicity of the sagittal height value from the center to the edge of the aspheric lens and the consistency of the sign are controlled to eliminate the irregular aspheric surface. A medium-wave infrared imaging lens is designed, and irregular aspheric surfaces appear in its initial design structure. The irregular aspheric surface is controlled by the method of controlling the sagittal height value and the narcissus suppression scheme. The optimized infrared imaging system has no irregular aspheric surface, and the narcissus energy returned to the detector after reflection from each surface of the lens covers the entire detector image surface, indicating that this optimization scheme is suitable for infrared systems with irregular aspheric surfaces and is more intuitive.