This paper through describing the comparison between LingAo Phrase II ATWT and Tomari DAS (Diverse Actuation System) in some aspects which including function, structure, and so on. Through the comparison, the author finds the biggest difference between the systems is the manual analog devices are used in ATWT. And the author proves the full digital control system’s performance is used to defense the CCF (Common Cause Failure). Especially the Controller be detailed analyzed by FTA (Failure Tree Analysis) and unavailability, because of the controller’s important. At last the author proposes better solutions for coping with the requirement of the Defense in CCF.