Abstract: To meet the control requirement of Direct-Drive Robot in which the large inertia variations exist,this paper presents a passive adaptive controller which reduces the sensitivity of the parameter variations.The conditions under which conventional controller parameters and passive adaptive controller parameters can be designed independently are derived.Experimental results show that the proposed method can get sigificant feature in presence of large variations of the electro-mechanical time constant of the object.The proposed method can be realized easily and may be applied in engineering.