<p>This paper proposes a design method of DOB/CDOB to improve the performance of the control system in the presence of variable time delay and disturbance. The control method using disturbance observer (DOB) can enhance robustness to parameter variations and disturbances by compensating the lumped equivalent disturbance. Disturbance rejection performance and stability mainly depend on the bandwidth determined by cutoff frequency of DOB’s Q-filter. The more bandwidth increases, the better disturbance rejection performance gets. However, when the system is implemented with hardware and software, the value of bandwidth for satisfying stability has constraint. On the other hand, as one of the methods to compensate variable time delay, communication disturbance observer (CDOB) has been proposed and widely applied as it does not require the time delay model. In the presence of network disturbance caused by variable time delay, the robust stability of the CDOB-based control system depends on the bandwidth of low-pass filter (LPF) and thus, determination of proper cutoff frequency is very important. Totally, the robust stability of control system with variable time delay and disturbance depends on cutoff frequencies of LPFs in DOB/CDOB. In order to resolve this problem, this paper will focus on determining the proper cutoff frequencies of LPFs in DOB/CDOB using stability condition of the DOB inner loop and the bound of model variation by variable time delay. The effectiveness of the proposed method is verified by experimental results.</p>