Most of KBE systems applied by previous researchers are dependent on some CAD software,which makes knowledge hard to be reused to other CAD software. Independent knowledge based system is independent of CAD software; therefore knowledge can be reused freely. This paper describes independent knowledge based system for mechanical design. A detailed discussion about typical design is put forward including design process implementation based on knowledge engineering,independent knowledge based design architecture. The main principal of knowledge driven engineering is explained. The implementation of KBE on the design of worm reducer is studied as a case. Independent knowledge based reducer design system is realized. The usage of independent knowledge based system makes KBE system work independent of CAD software,which enhances their portability and fertilizes the collaborative work of heterogeneous CAD systems. Most of KBE systems applied by previous researchers are dependent on some CAD software, which makes knowledge hard to be reused to other CAD software. Independent knowledge based system is independent of CAD software; therefore knowledge can be reused freely. This paper describes independent knowledge based system for mechanical design. A detailed discussion about typical design is put forward including design process implementation based on knowledge engineering, independent knowledge based design architecture. The main principle of knowledge driven engineering is explained. The implementation of KBE on the design of worm reducer is studied as a case. Independent usage based on reducer design system is realized. The usage of independent knowledge based system makes KBE system work independent of CAD software, which enhances their portability and fertilizes the collaborative work of heterogeneous CAD systems.