Reflective optical systems have small size, light weight and excellent imaging performance, which makes it very popular in space remote sensing systems. The third order aberration expression and basic design process of four-mirror system are given by aberration analysis based on PW method. Two space remote sensing systems using coaxial and abaxial four-mirror system is designed under the guidance of the aberration theory. The two systems have excellent imaging performance. The systems have compact structure and the physical length to the EFL ratio is about 1/6.4. Both of the size and weight meet the technical requirements, the correctness and practicality of the theoretical analysis are proved.